Reversing single linked list in C#

Reversing single linked list in C# - c#

I am trying to reverse a linked list. This is the code I have come up with:
public static void Reverse(ref Node root)
{
Node tmp = root;
Node nroot = null;
Node prev = null;
while (tmp != null)
{
//Make a new node and copy tmp
nroot = new Node();
nroot.data = tmp.data;
nroot.next = prev;
prev = nroot;
tmp = tmp.next;
}
root = nroot;
}
It is working well. Was wondering if it possible to avoid creating new node. Would like to have suggestions on this.

That question gets asked a lot. When I was asked it in my interviews many years ago, I reasoned as follows: a singly-linked list is essentially a stack. Reversing a linked list is therefore a trivial operation on stacks:
newList = emptyList;
while(!oldList.IsEmpty())
newList.Push(oldList.Pop());
Now all you have to do is implement IsEmpty and Push and Pop, which are one or two lines tops.
I wrote that out in about twenty seconds and the interviewer seemed somewhat perplexed at that point. I think he was expecting me to take about twenty minutes to do about twenty seconds work, which has always seemed odd to me.

Node p = root, n = null;
while (p != null) {
Node tmp = p.next;
p.next = n;
n = p;
p = tmp;
}
root = n;

Years ago I missed out on a hipster-L.A.-entertainment-company ASP.NET MVC developer position because I could not answer this question :( (It's a way to weed out non-computer-science majors.) So I am embarrassed to admit that it took me way too long to figure this out in LINQpad using the actual LinkedList<T>:
var linkedList = new LinkedList<int>(new[]{1,2,3,4,5,6,7,8,9,10});
linkedList.Dump("initial state");
var head = linkedList.First;
while (head.Next != null)
{
var next = head.Next;
linkedList.Remove(next);
linkedList.AddFirst(next.Value);
}
linkedList.Dump("final state");
The read-only LinkedListNode<T>.Next property is what makes LinkedList<T> so important here. (Non-comp-sci people are encouraged to study the history of Data Structures---we are supposed to ask the question, Where does the linked list come from---why does it exist?)

You don't need to make a copy. Some pseudo code:
prev = null;
current = head;
next = current->next;
(while next != null)
current->next=prev
prev=current
current=next
next=current->next

This performed pretty well on Leetcode.
public ListNode ReverseList(ListNode head) {
ListNode previous = null;
ListNode current = head;
while(current != null) {
ListNode nextTemp = current.next;
current.next = previous;
previous = current;
current = nextTemp;
}
return previous;
}

Why not just have the head point at the tail, the tail point at the head, and go through the list reversing the direction in which prev points?
If you're not using a head and a tail, just go through the list reversing the prev relationships, and then make head point at the one that had a null prev when you got to it.

public Node ReverseList(Node cur, Node prev)
{
if (cur == null) // if list is null
return cur;
Node n = cur.NextNode;
cur.NextNode = prev;
return (n == null) ? cur : ReverseList(n, cur);
}

Here a sample code to reverse a linked list.
using System;
class Program
{
static void Main(string[] args)
{
LinkItem item = generateLinkList(5);
printLinkList(item);
Console.WriteLine("Reversing the list ...");
LinkItem newItem = reverseLinkList(item);
printLinkList(newItem);
Console.ReadLine();
}
static public LinkItem generateLinkList(int total)
{
LinkItem item = new LinkItem();
for (int number = total; number >=1; number--)
{
item = new LinkItem
{
name = string.Format("I am the link item number {0}.", number),
next = (number == total) ? null : item
};
}
return item;
}
static public void printLinkList(LinkItem item)
{
while (item != null)
{
Console.WriteLine(item.name);
item = item.next;
}
}
static public LinkItem reverseLinkList(LinkItem item)
{
LinkItem newItem = new LinkItem
{
name = item.name,
next = null
};
while (item.next != null)
{
newItem = new LinkItem
{
name = item.next.name,
next = newItem
};
item = item.next;
}
return newItem;
}
}
class LinkItem
{
public string name;
public LinkItem next;
}

linked list reversal recursive
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ReverseLinkedList
{
class Program
{
static void Main(string[] args)
{
Node head = null;
LinkedList.Append(ref head, 25);
LinkedList.Append(ref head, 5);
LinkedList.Append(ref head, 18);
LinkedList.Append(ref head, 7);
Console.WriteLine("Linked list:");
LinkedList.Print(head);
Console.WriteLine();
Console.WriteLine("Reversed Linked list:");
LinkedList.Reverse(ref head);
LinkedList.Print(head);
Console.WriteLine();
Console.WriteLine("Reverse of Reversed Linked list:");
LinkedList.ReverseUsingRecursion(head);
head = LinkedList.newHead;
LinkedList.PrintRecursive(head);
}
public static class LinkedList
{
public static void Append(ref Node head, int data)
{
if (head != null)
{
Node current = head;
while (current.Next != null)
{
current = current.Next;
}
current.Next = new Node();
current.Next.Data = data;
}
else
{
head = new Node();
head.Data = data;
}
}
public static void Print(Node head)
{
if (head == null) return;
Node current = head;
do
{
Console.Write("{0} ", current.Data);
current = current.Next;
} while (current != null);
}
public static void PrintRecursive(Node head)
{
if (head == null)
{
Console.WriteLine();
return;
}
Console.Write("{0} ", head.Data);
PrintRecursive(head.Next);
}
public static void Reverse(ref Node head)
{
if (head == null) return;
Node prev = null, current = head, next = null;
while (current.Next != null)
{
next = current.Next;
current.Next = prev;
prev = current;
current = next;
}
current.Next = prev;
head = current;
}
public static Node newHead;
public static void ReverseUsingRecursion(Node head)
{
if (head == null) return;
if (head.Next == null)
{
newHead = head;
return;
}
ReverseUsingRecursion(head.Next);
head.Next.Next = head;
head.Next = null;
}
}
public class Node
{
public int Data = 0;
public Node Next = null;
}
}
}

Complexity O(n+m). Assuming head is the start node:
List<Node>Nodes = new List<Node>();
Node traverse= root;
while(traverse!=null)
{
Nodes.Add(traverse);
traverse = traverse.Next;
}
int i = Nodes.Count - 1;
root = Nodes[i];
for(; i>0; i--)
{
Nodes[i].Next = Nodes[i-1];
}
Nodes[0].Next=null;

In case you want a ready-made efficient implementation, I created an alternative to LinkedList that supports enumeration and reverse operations. https://github.com/NetFabric/NetFabric.DoubleLinkedList

public class Node<T>
{
public T Value { get; set; }
public Node<T> Next { get; set; }
}
public static Node<T> Reverse<T>(Node<T> head)
{
Node<T> tail = null;
while(head!=null)
{
var node = new Node<T> { Value = head.Value, Next = tail };
tail = node;
head = head.Next;
}
return tail;
}

The definition of ref is unnecessary because if you make the node as a reference type, it is OK to do:
public static void Reverse(Node root)
Also, the beauty of the interview question is less consumption of memory and in place reversal. Maybe a recursive way of doing it is also asked.

Related

Rotate Doubly Linked List

I am trying to rotate a doubly linked list both clockwise and counter clockwise. However my code only outputting a part of the list. I understand that the list should not rotate if there are 0 or 1 elements. I would like to rotate to the right if the value is greater than 1. Also, I would like to rotate to the left if the value is less than 0. I'm not sure what I have done wrong with my list. The logic is very confusing. The addLast method has intentionally not been included since it works.
public class Node
{
public Node next;
public Node previous;
public Object data;
}
public class LinkedList
{
private Node head;
private Node tail;
public Node rotate(int k)
{
if (head == null )
{
return head;
}
Node node = head;
k = k % listSize(head);
if (k == 0 || k == 1)
{
return head;
}
//Rotates
while (node != null && k > 1)
{
node = node.next;
k--;
}
Node newhead = node.next;
newhead.previous = null;
node.next = null;
Node temp = newhead;
while (temp.next != null)
{
temp = temp.next;
}
newhead = head;
node.previous = temp.previous;
tail = node;
return newhead;
}
public int listSize(Node node)
{
if(node == null)
{
return 0;
}
int count = 0;
while(node != null)
{
count++;
node = node.next;
}
return count;
}
public void addLast(Object data)
{
Node toAdd = new Node();
toAdd.data = data;
toAdd.next = null;
if (head == null)
{
head = toAdd;
tail = null;
}
else
{
if (tail == null)
{
head.next = toAdd;
tail = toAdd;
}
else
{
tail.next = toAdd;
tail = toAdd;
}
}
}
}
static void Main(string[] args)
{
Console.WriteLine("Add Last: ");
LinkedList myList2 = new LinkedList();
myList2.addLast("Tim");
myList2.addLast("Nick");
myList2.addLast("Julie");
myList2.addLast("Jessie");
myList2.addLast("Jordan");
myList2.addLast("Peter");
myList2.addLast("John");
myList2.rotate(2);
}
Edit: I have tried rewriting my code before reading any comments. It still does rotate the list successfully.

Yes, it's tough, and I had many of the same problems. One thing that helped was renaming some of the variables to make it clear in my head what was going on.
In the rotate function:
public Node rotate(int k)
{
if (head == null)
{
return head;
}
k = -k;
k = k % listSize(head);
if (k<0) { k+= listSize(head); }
if (k == 0 )
{
return head;
}
//Rotates
Node newhead = head;
while (newhead != null && k > 0)
{
newhead = newhead.next;
k--;
}
Node newtail = newhead.previous;
newhead.previous = null;
newtail.next = null;
tail.next = head;
head.previous = tail;
head = newhead;
tail = newtail;
return newhead;
}
(This assumes you're keeping the tail updated in addLast(). If you are, you may as well use it. Here's what I had:)
public void addLast(Object inData)
{
Node node = new Node();
node.next = null;
node.data = inData;
node.previous = tail;
if (head == null)
{
head = node;
}
if (tail != null)
{
tail.next = node;
}
tail = node;
}
I hope this is clearer.

One of the things I think you're missing is that anytime you set one nodes Next property, you should also set the corresponding next node's Previous property. Just doing that may help with the list navigation.
Otherwise, it can be helpful to break down the tasks into more discreet methods, so there's not too much going on in one method.
One thing that may be helpful, for example, is to add a method that returns a node at a specific index. This allows us to easily grab a node and set it to the new Head, which means our Rotate method doesn't need a loop - it just gets the node at the appropriate index and sets that node as the new head.
Note that setting a node as a new Head node should also be broken out into a new method, since there's a fair amount involved there as well (a new head means a new tail, and lots of Previous and Next properties to think about).
Hopefully this implementation based on your code is instructive. Please let me know if something doesn't make sense:
public class Node
{
public object Data { get; set; }
public Node Next { get; set; }
public Node Previous { get; set; }
public Node(object data)
{
Data = data;
}
public override string ToString()
{
return Data.ToString();
}
}
public class LinkedList
{
public Node Head { get; private set; }
public Node Tail { get; private set; }
public int Count
{
get
{
var count = 0;
for (var n = Head; n != null; n = n.Next, count++) ;
return count;
}
}
private void AddFirst(object data)
{
var node = new Node(data) {Next = Head?.Next};
if (Head != null) { Head.Previous = node;}
if (Tail == null) Tail = node;
Head = node;
}
public void Add(object data)
{
if (Head == null)
{
AddFirst(data);
}
else
{
var node = new Node(data) {Previous = Tail?.Previous};
if (Tail != null) Tail.Next = node;
node.Previous = Tail;
Tail = node;
}
}
private Node ItemAt(int index)
{
var item = Head;
while (index-- > 0) item = item.Next;
return item;
}
private void SetNewHead(int indexOfNewHead)
{
var newHead = ItemAt(indexOfNewHead);
var newTail = newHead.Previous;
var oldHead = Head;
var oldTail = Tail;
newHead.Previous = null;
newTail.Next = null;
oldTail.Next = oldHead;
oldHead.Previous = oldTail;
Head = newHead;
Tail = newTail;
}
/// <summary>
/// Rotates the Tail to the Head the specified number of times
/// </summary>
/// <param name="rotations">
/// The number of times to rotate the Tail to the Head
/// A negative number rotates the Head to the Tail
/// </param>
public void Rotate(int rotations)
{
var count = Count;
rotations = rotations % count;
if (rotations == 0) return;
// Find the index of the new head based on the number of rotations
// If rotations is positive, then the index is the count minus rotations
// If rotations is negative, then the index is 'rotations * -1' (or -rotations)
var newHeadIndex = rotations > 0 ? count - rotations : -rotations;
// Now that we know the index of the new head, we just set it as the head
SetNewHead(newHeadIndex);
}
public List<Node> ToList()
{
var nodes = new List<Node>();
for (var node = Head; node != null; node = node.Next)
{
nodes.Add(node);
}
return nodes;
}
public override string ToString()
{
return Count == 0 ? "{no items}" : "'" + string.Join("' <-> '", ToList()) + "'";
}
}
And here's a sample program that lets you enter some data and then rotate the list:
public static void Main(string[] args)
{
var linkedList = new LinkedList();
while (true)
{
var data = GetStringFromUser("Enter data to add, or 'exit' to stop: ");
if (data.Equals("exit", StringComparison.OrdinalIgnoreCase))
break;
linkedList.Add(new Node(data));
}
Console.WriteLine("\nLinked list items:");
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine(linkedList);
Console.ResetColor();
while (true)
{
var rotations = GetIntFromUser("\nEnter number of rotations, or 42 to stop: ");
if (rotations == 42) break;
linkedList.Rotate(rotations);
Console.WriteLine($"\nLinked list items after {rotations} rotations:");
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine(linkedList);
Console.ResetColor();
}
}
The code above uses the following helper methods:
public static string GetStringFromUser(string prompt)
{
Console.Write(prompt);
return Console.ReadLine();
}
public static int GetIntFromUser(string prompt, Func<double, bool> validator = null)
{
bool isValid = true;
int result;
do
{
if (!isValid)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Invalid input, please try again.");
Console.ResetColor();
}
else isValid = false;
Console.Write(prompt);
} while (!int.TryParse(Console.ReadLine(), out result) &&
(validator == null || !validator.Invoke(result)));
return result;
}
Sample Output

LinkedList Implementation Bug

I tried to implement my linked list below, It just that when I used my linked list, it seems that it's inserting a null entry in the middle. Anyone could take a look? The problem could be in the add end method.
LinkedList<T>
public class LinkedList<T> : IEnumerable<T>
{
public Node<T> Head { get; set; }
public int Count { get; set; }
public LinkedList()
{
Head = new Node<T>();
}
public void AddStart(T data)
{
if (Head == null)
{
Head = new Node<T> {Value = data};
}
else
{
var newNode = new Node<T> {Value = data, Next = Head};
Head = newNode;
}
Count++;
}
public void AddEnd(T data)
{
var newNode = new Node<T> { Value = data, Next = null};
var current = Head;
if (Head == null)
{
Head = newNode;
}
else
{
while (current.Next != null)
{
current = current.Next;
}
current.Next = newNode;
}
}
public IEnumerator<T> GetEnumerator()
{
Node<T> current = Head;
while (current != null)
{
yield return current.Value;
current = current.Next;
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
Usage:
LinkedList<string> strings = new LinkedList<string>();
strings.AddStart("a");
strings.AddStart("b");
strings.AddStart("c");
strings.AddEnd("a");
strings.AddEnd("e");
strings.AddEnd("d");
Result: (Notice the null in the middle)
c
b
a
a
e
d
Usage:
LinkedList<string> strings = new LinkedList<string>();
strings.AddStart("a");
strings.AddStart("b");
strings.AddStart("c");
strings.AddEnd("a");
strings.AddEnd("e");
strings.AddEnd("d");
strings.AddStart("a");
strings.AddEnd("b");
strings.AddStart("a");
strings.AddStart("b");
strings.AddStart("c");
strings.AddEnd("a");
strings.AddEnd("e");
strings.AddEnd("d");
Result: (Notice the null in the middle)
c
b
a
a
c
b
a
a
e
d
b
a
e
d

You are creating an empty Node, when you initialize your LinkedList:
public LinkedList()
{
Head = new Node<T>();
}
At this point you essentially have a node without a value. This is displayed as an empty value.
Everytime you call AddStart, you insert items before hand. When calling AddEnd you insert items at the end. Since you call both methods equally, it appears that the initial node is in the middle.
You can resolve this by changing your constructor to this:
public LinkedList()
{
Head = null;
}
Or by removing the constructor alltogether. In both methods you are checking for a Head node with a value, so you do not need to initialize it without a value.
if (Head == null)
{
Head = new Node<T> {Value = data};
}
In your current state, you are checking if Head is null. Head is of Type Node, which, if it is a class, cannot be null, if you initialize it in your constrcutor (Head = new Node<T>(); //not null any longer). So you need to make up your mind on how you want to solve it.
Personally I'd just write a unit test to assert my logic and implementation is correct. If you assume that Head is null after initialisation, test for it:
[Fact]
public void AssertHeadIsNull()
{
var list = new LinkedList<int>();
Assert.Null(list.Head);
}
In your case, the test would have failed, and you could have backtracked the issue to your constructor.

Remove First from linked List

I am trying to Remove my first value in my linked List y but i am not sure if my code is right my remove last is working fine but my removeFirst is not.
public class IntegerLinkedList
{
private class Node
{
public int value;
public Node next;
public Node(int v)
{
value = v;
next = null;
}
internal int removeLast()
{
int value;
if (next.next == null)
{
value = next.value;
next = null;
return value;
}
else
return next.removeLast();
}
internal int removeFirst()
{
int value;
if (next.next != null)
{
value = next.value;
next = null;
return value;
}
else
return next.removeFirst();
}
}
int count;
Node start;
here is my code for removeFirst
public int removeFirst()
{
int value;
if (start.next != null)
{
value = start.value;
}
else
value = start.removeFirst();
return value;
}
}
here is my link list
IntegerLinkedList myList = new IntegerLinkedList();
myList.addFirst(1);
myList.addFirst(2);
myList.addFirst(3);
myList.addFirst(4);
Console.WriteLine(" expect to 4 to be removed" + myList.removeFirst());
}
it displays
removed 4 but i am not sure if thats correct

This code:
internal int removeFirst()
{
int value;
if (next.next != null)
{
value = next.value;
next = null;
return value;
}
else
return next.removeFirst();
}
Is going to recursively traverse the list and cutoff the last element. It is effectively the same as removeLast.
Instead, you need to just do something like this:
Node currentStart = start;
start = start.next;
return currentStart.value;
The "start" Node object should no longer have any references pointing at it, so it will be GCd.
A quick note; you should likely remove "RemoveFirst" and "RemoveLast" from your Node class. Those are functions of the list; not nodes.
If you put all the methods in the list class (as you should!), addFirst (should be AddFirst) would be:
public void AddFirst(int item)
{
Node newNode = new Node();
newNode.value = item;
newNode.next = start;
start = newNode;
}
Your addLast requires iteration (or for you to track the "tail" node, your choice):
public void AddLast(int item)
{
Node newNode = new Node();
newNode.value = item;
Node tailNode = start;
while (tailNode.next != null)
tailNode = tailNode.next;
//In C++ you could cheat and do: while (tailNode = tailNode.next != null);
//Tail node is now at the end
tailNode.next = newNode;
}

Breadth-first traversal

I was trying to solve one interview question, but for that I have to travel the binary tree level by level. I have designed BinaryNode with having below variable
private object data;
private BinaryNode left;
private BinaryNode right;
Could someone please help to write the BreadthFirstSearch method inside my BinarySearchTree class?
Update: Thanks everyone for your inputs. So this was the interview question.
"Given a binary search tree, design an algorithm which creates a linked list of all the nodes at each depth (i.e., if you have a tree with depth D, you’ll have D linked lists)".
Here is my Method, let me know your expert comment.
public List<LinkedList<BNode>> FindLevelLinkList(BNode root)
{
Queue<BNode> q = new Queue<BNode>();
// List of all nodes starting from root.
List<BNode> list = new List<BNode>();
q.Enqueue(root);
while (q.Count > 0)
{
BNode current = q.Dequeue();
if (current == null)
continue;
q.Enqueue(current.Left);
q.Enqueue(current.Right);
list.Add(current);
}
// Add tree nodes of same depth into individual LinkedList. Then add all LinkedList into a List
LinkedList<BNode> LL = new LinkedList<BNode>();
List<LinkedList<BNode>> result = new List<LinkedList<BNode>>();
LL.AddLast(root);
int currentDepth = 0;
foreach (BNode node in list)
{
if (node != root)
{
if (node.Depth == currentDepth)
{
LL.AddLast(node);
}
else
{
result.Add(LL);
LL = new LinkedList<BNode>();
LL.AddLast(node);
currentDepth++;
}
}
}
// Add the last linkedlist
result.Add(LL);
return result;
}

A breadth first search is usually implemented with a queue, a depth first search using a stack.
Queue<Node> q = new Queue<Node>();
q.Enqueue(root);
while(q.Count > 0)
{
Node current = q.Dequeue();
if(current == null)
continue;
q.Enqueue(current.Left);
q.Enqueue(current.Right);
DoSomething(current);
}
As an alternative to checking for null after dequeuing you can check before adding to the Queue. I didn't compile the code, so it might contain some small mistakes.
A fancier (but slower) version that integrates well with LINQ:
public static IEnumerable<T> BreadthFirstTopDownTraversal<T>(T root, Func<T, IEnumerable<T>> children)
{
var q = new Queue<T>();
q.Enqueue(root);
while (q.Count > 0)
{
T current = q.Dequeue();
yield return current;
foreach (var child in children(current))
q.Enqueue(child);
}
}
Which can be used together with a Children property on Node:
IEnumerable<Node> Children { get { return new []{ Left, Right }.Where(x => x != null); } }
...
foreach(var node in BreadthFirstTopDownTraversal(root, node => node.Children))
{
...
}

var queue = new Queue<BinaryNode>();
queue.Enqueue(rootNode);
while(queue.Any())
{
var currentNode = queue.Dequeue();
if(currentNode.data == searchedData)
{
break;
}
if(currentNode.Left != null)
queue.Enqueue(currentNode.Left);
if(currentNode.Right != null)
queue.Enqueue(currentNode.Right);
}

using DFS approach: The tree traversal is O(n)
public class NodeLevel
{
public TreeNode Node { get; set;}
public int Level { get; set;}
}
public class NodeLevelList
{
private Dictionary<int,List<TreeNode>> finalLists = new Dictionary<int,List<TreeNode>>();
public void AddToDictionary(NodeLevel ndlvl)
{
if(finalLists.ContainsKey(ndlvl.Level))
{
finalLists[ndlvl.Level].Add(ndlvl.Node);
}
else
{
finalLists.Add(ndlvl.Level,new List<TreeNode>(){ndlvl.Node});
}
}
public Dictionary<int,List<TreeNode>> GetFinalList()
{
return finalLists;
}
}
The method that does traversal:
public static void DFSLevel(TreeNode root, int level, NodeLevelList nodeLevelList)
{
if(root == null)
return;
nodeLevelList.AddToDictionary(new NodeLevel{Node = root, Level = level});
level++;
DFSLevel(root.Left,level,nodeLevelList);
DFSLevel(root.Right,level,nodeLevelList);
}

Creating a very simple linked list

I am trying to create a linked list just to see if I can, and I am having trouble getting my head around it. Does anyone have an example of a very simple implementation of Linked list using C#? All the examples I have found so far are quite overdone.

A Linked List, at its core is a bunch of Nodes linked together.
So, you need to start with a simple Node class:
public class Node {
public Node next;
public Object data;
}
Then your linked list will have as a member one node representing the head (start) of the list:
public class LinkedList {
private Node head;
}
Then you need to add functionality to the list by adding methods. They usually involve some sort of traversal along all of the nodes.
public void printAllNodes() {
Node current = head;
while (current != null)
{
Console.WriteLine(current.data);
current = current.next;
}
}
Also, inserting new data is another common operation:
public void Add(Object data) {
Node toAdd = new Node();
toAdd.data = data;
Node current = head;
// traverse all nodes (see the print all nodes method for an example)
current.next = toAdd;
}
This should provide a good starting point.

Based on what #jjnguy said, here's the full Console App example:
public class Node
{
public Node next;
public Object data;
}
public class LinkedList
{
private Node head;
public void printAllNodes()
{
Node current = head;
while (current != null)
{
Console.WriteLine(current.data);
current = current.next;
}
}
public void AddFirst(Object data)
{
Node toAdd = new Node();
toAdd.data = data;
toAdd.next = head;
head = toAdd;
}
public void AddLast(Object data)
{
if (head == null)
{
head = new Node();
head.data = data;
head.next = null;
}
else
{
Node toAdd = new Node();
toAdd.data = data;
Node current = head;
while (current.next != null)
{
current = current.next;
}
current.next = toAdd;
}
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Add First:");
LinkedList myList1 = new LinkedList();
myList1.AddFirst("Hello");
myList1.AddFirst("Magical");
myList1.AddFirst("World");
myList1.printAllNodes();
Console.WriteLine();
Console.WriteLine("Add Last:");
LinkedList myList2 = new LinkedList();
myList2.AddLast("Hello");
myList2.AddLast("Magical");
myList2.AddLast("World");
myList2.printAllNodes();
Console.ReadLine();
}
}

This one is nice:
namespace ConsoleApplication1
{
// T is the type of data stored in a particular instance of GenericList.
public class GenericList<T>
{
private class Node
{
// Each node has a reference to the next node in the list.
public Node Next;
// Each node holds a value of type T.
public T Data;
}
// The list is initially empty.
private Node head = null;
// Add a node at the beginning of the list with t as its data value.
public void AddNode(T t)
{
Node newNode = new Node();
newNode.Next = head;
newNode.Data = t;
head = newNode;
}
// The following method returns the data value stored in the last node in
// the list. If the list is empty, the default value for type T is
// returned.
public T GetFirstAdded()
{
// The value of temp is returned as the value of the method.
// The following declaration initializes temp to the appropriate
// default value for type T. The default value is returned if the
// list is empty.
T temp = default(T);
Node current = head;
while (current != null)
{
temp = current.Data;
current = current.Next;
}
return temp;
}
}
}
Test code:
static void Main(string[] args)
{
// Test with a non-empty list of integers.
GenericList<int> gll = new GenericList<int>();
gll.AddNode(5);
gll.AddNode(4);
gll.AddNode(3);
int intVal = gll.GetFirstAdded();
// The following line displays 5.
System.Console.WriteLine(intVal);
}
I encountered it on msdn here

Here is one with IEnumerable and a Recursive Reverse method though it is no faster than the while loop in the Reverse method both are O(n):
public class LinkedList<T> : IEnumerable
{
private Node<T> _head = null;
public Node<T> Add(T value)
{
var node = new Node<T> {Value = value};
if (_head == null)
{
_head = node;
}
else
{
var current = _head;
while (current.Next != null)
{
current = current.Next;
}
current.Next = node; //new head
}
return node;
}
public T Remove(Node<T> node)
{
if (_head == null)
return node.Value;
if (_head == node)
{
_head = _head.Next;
node.Next = null;
return node.Value;
}
var current = _head;
while (current.Next != null)
{
if (current.Next == node)
{
current.Next = node.Next;
return node.Value;
}
current = current.Next;
}
return node.Value;
}
public void Reverse()
{
Node<T> prev = null;
var current = _head;
if (current == null)
return;
while (current != null)
{
var next = current.Next;
current.Next = prev;
prev = current;
current = next;
}
_head = prev;
}
public void ReverseRecursive()
{
reverseRecursive(_head, null);
}
private void reverseRecursive(Node<T> current, Node<T> prev)
{
if (current.Next == null)
{
_head = current;
_head.Next = prev;
return;
}
var next = current.Next;
current.Next = prev;
reverseRecursive(next, current);
}
public IEnumerator<T> Enumerator()
{
var current = _head;
while (current != null)
{
yield return current.Value;
current = current.Next;
}
}
public IEnumerator GetEnumerator()
{
return Enumerator();
}
}
public class Node<T>
{
public T Value { get; set; }
public Node<T> Next { get; set; }
}

I am a beginner and this helped me:
class List
{
private Element Root;
}
First you create the class List which will contain all the methods.
Then you create the Node-Class, I will call it Element
class Element
{
public int Value;
public Element Next;
}
Then you can start adding methods to your List class. Here is a 'add' method for example.
public void Add(int value)
{
Element newElement = new Element();
newElement.Value = value;
Element rootCopy = Root;
Root = newElement;
newElement.Next = rootCopy;
Console.WriteLine(newElement.Value);
}

public class Node
{
private Object data;
public Node next {get;set;}
public Node(Object data)
{
this.data = data;
}
}
public class Linkedlist
{
Node head;
public void Add(Node n)
{
n.Next = this.Head;
this.Head = n;
}
}
using:
LinkedList sample = new LinkedList();
sample.add(new Node("first"));
sample.Add(new Node("second"))

I am giving an extract from the book "C# 6.0 in a Nutshell by Joseph Albahari and Ben Albahari"
Here’s a demonstration on the use of LinkedList:
var tune = new LinkedList<string>();
tune.AddFirst ("do"); // do
tune.AddLast ("so"); // do - so
tune.AddAfter (tune.First, "re"); // do - re- so
tune.AddAfter (tune.First.Next, "mi"); // do - re - mi- so
tune.AddBefore (tune.Last, "fa"); // do - re - mi - fa- so
tune.RemoveFirst(); // re - mi - fa - so
tune.RemoveLast(); // re - mi - fa
LinkedListNode<string> miNode = tune.Find ("mi");
tune.Remove (miNode); // re - fa
tune.AddFirst (miNode); // mi- re - fa
foreach (string s in tune) Console.WriteLine (s);

Here is a good implementation.
It is short, but implemented Add(x), Delete(x), Contain(x) and Print().
It avoid special process when add to empty list or delete the first element.
While most of other examples did special process when delete the first element.
The list can contain any data type.
using System;
class Node<Type> : LinkedList<Type>
{ // Why inherit from LinkedList? A: We need to use polymorphism.
public Type value;
public Node(Type value) { this.value = value; }
}
class LinkedList<Type>
{
Node<Type> next; // This member is treated as head in class LinkedList, but treated as next element in class Node.
/// <summary> if x is in list, return previos pointer of x. (We can see any class variable as a pointer.)
/// if not found, return the tail of the list. </summary>
protected LinkedList<Type> Previos(Type x)
{
LinkedList<Type> p = this; // point to head
for (; p.next != null; p = p.next)
if (p.next.value.Equals(x))
return p; // find x, return the previos pointer.
return p; // not found, p is the tail.
}
/// <summary> return value: true = success ; false = x not exist </summary>
public bool Contain(Type x) { return Previos(x).next != null ? true : false; }
/// <summary> return value: true = success ; false = fail to add. Because x already exist.
/// </summary> // why return value? If caller want to know the result, they don't need to call Contain(x) before, the action waste time.
public bool Add(Type x)
{
LinkedList<Type> p = Previos(x);
if (p.next != null) // Find x already in list
return false;
p.next = new Node<Type>(x);
return true;
}
/// <summary> return value: true = success ; false = x not exist </summary>
public bool Delete(Type x)
{
LinkedList<Type> p = Previos(x);
if (p.next == null)
return false;
//Node<Type> node = p.next;
p.next = p.next.next;
//node.Dispose(); // GC dispose automatically.
return true;
}
public void Print()
{
Console.Write("List: ");
for (Node<Type> node = next; node != null; node = node.next)
Console.Write(node.value.ToString() + " ");
Console.WriteLine();
}
}
class Test
{
static void Main()
{
LinkedList<int> LL = new LinkedList<int>();
if (!LL.Contain(0)) // Empty list
Console.WriteLine("0 is not exist.");
LL.Print();
LL.Add(0); // Add to empty list
LL.Add(1); LL.Add(2); // attach to tail
LL.Add(2); // duplicate add, 2 is tail.
if (LL.Contain(0))// Find existed element which is head
Console.WriteLine("0 is exist.");
LL.Print();
LL.Delete(0); // Delete head
LL.Delete(2); // Delete tail
if (!LL.Delete(0)) // Delete non-exist element
Console.WriteLine("0 is not exist.");
LL.Print();
Console.ReadLine();
}
}
By the way, the implementation in
http://www.functionx.com/csharp1/examples/linkedlist.htm
have some problem:
Delete() will fail when there is only 1 element.
(Throw exception at line "Head.Next = Current.Next;" because Current is null.)
Delete(position) will fail when deleting first element,
In other words, call Delete(0) will fail.

Dmytro did a good job, but here is a more concise version.
class Program
{
static void Main(string[] args)
{
LinkedList linkedList = new LinkedList(1);
linkedList.Add(2);
linkedList.Add(3);
linkedList.Add(4);
linkedList.AddFirst(0);
linkedList.Print();
}
}
public class Node
{
public Node(Node next, Object value)
{
this.next = next;
this.value = value;
}
public Node next;
public Object value;
}
public class LinkedList
{
public Node head;
public LinkedList(Object initial)
{
head = new Node(null, initial);
}
public void AddFirst(Object value)
{
head = new Node(head, value);
}
public void Add(Object value)
{
Node current = head;
while (current.next != null)
{
current = current.next;
}
current.next = new Node(null, value);
}
public void Print()
{
Node current = head;
while (current != null)
{
Console.WriteLine(current.value);
current = current.next;
}
}
}

public class DynamicLinkedList
{
private class Node
{
private object element;
private Node next;
public object Element
{
get { return this.element; }
set { this.element = value; }
}
public Node Next
{
get { return this.next; }
set { this.next = value; }
}
public Node(object element, Node prevNode)
{
this.element = element;
prevNode.next = this;
}
public Node(object element)
{
this.element = element;
next = null;
}
}
private Node head;
private Node tail;
private int count;
public DynamicLinkedList()
{
this.head = null;
this.tail = null;
this.count = 0;
}
public void AddAtLastPosition(object element)
{
if (head == null)
{
head = new Node(element);
tail = head;
}
else
{
Node newNode = new Node(element, tail);
tail = newNode;
}
count++;
}
public object GetLastElement()
{
object lastElement = null;
Node currentNode = head;
while (currentNode != null)
{
lastElement = currentNode.Element;
currentNode = currentNode.Next;
}
return lastElement;
}
}
Testing with:
static void Main(string[] args)
{
DynamicLinkedList list = new DynamicLinkedList();
list.AddAtLastPosition(1);
list.AddAtLastPosition(2);
list.AddAtLastPosition(3);
list.AddAtLastPosition(4);
list.AddAtLastPosition(5);
object lastElement = list.GetLastElement();
Console.WriteLine(lastElement);
}

public class Node<T>
{
public T item;
public Node<T> next;
public Node()
{
this.next = null;
}
}
class LinkList<T>
{
public Node<T> head { get; set; }
public LinkList()
{
this.head = null;
}
public void AddAtHead(T item)
{
Node<T> newNode = new Node<T>();
newNode.item = item;
if (this.head == null)
{
this.head = newNode;
}
else
{
newNode.next = head;
this.head = newNode;
}
}
public void AddAtTail(T item)
{
Node<T> newNode = new Node<T>();
newNode.item = item;
if (this.head == null)
{
this.head = newNode;
}
else
{
Node<T> temp = this.head;
while (temp.next != null)
{
temp = temp.next;
}
temp.next = newNode;
}
}
public void DeleteNode(T item)
{
if (this.head.item.Equals(item))
{
head = head.next;
}
else
{
Node<T> temp = head;
Node<T> tempPre = head;
bool matched = false;
while (!(matched = temp.item.Equals(item)) && temp.next != null)
{
tempPre = temp;
temp = temp.next;
}
if (matched)
{
tempPre.next = temp.next;
}
else
{
Console.WriteLine("Value not found!");
}
}
}
public bool searchNode(T item)
{
Node<T> temp = this.head;
bool matched = false;
while (!(matched = temp.item.Equals(item)) && temp.next != null)
{
temp = temp.next;
}
return matched;
}
public void DisplayList()
{
Console.WriteLine("Displaying List!");
Node<T> temp = this.head;
while (temp != null)
{
Console.WriteLine(temp.item);
temp = temp.next;
}
}
}

Add a Node class.
Then add a LinkedList class to implement the linked list
Add a test class to execute the linked list
namespace LinkedListProject
{
public class Node
{
public Node next;
public object data;
}
public class MyLinkedList
{
Node head;
public Node AddNodes(Object data)
{
Node node = new Node();
if (node.next == null)
{
node.data = data;
node.next = head;
head = node;
}
else
{
while (node.next != null)
node = node.next;
node.data = data;
node.next = null;
}
return node;
}
public void printnodes()
{
Node current = head;
while (current.next != null)
{
Console.WriteLine(current.data);
current = current.next;
}
Console.WriteLine(current.data);
}
}
[TestClass]
public class LinkedListExample
{
MyLinkedList linkedlist = new MyLinkedList();
[TestMethod]
public void linkedlisttest()
{
linkedlist.AddNodes("hello");
linkedlist.AddNodes("world");
linkedlist.AddNodes("now");
linkedlist.printnodes();
}
}
}

simple c# program to implement Single Link List with operations AddItemStart, AddItemEnd, RemoveItemStart, RemoveItemEnd and DisplayAllItems
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace SingleLinkedList
{
class Program
{
Node head;
Node current;
int counter = 0;
public Program()
{
head = new Node();
current = head;
}
public void AddStart(object data)
{
Node newnode = new Node();
newnode.next = head.next;
newnode.data = data;
head.next = newnode;
counter++;
}
public void AddEnd(object data)
{
Node newnode = new Node();
newnode.data = data;
current.next = newnode;
current = newnode;
counter++;
}
public void RemoveStart()
{
if (counter > 0)
{
head.next = head.next.next;
counter--;
}
else
{
Console.WriteLine("No element exist in this linked list.");
}
}
public void RemoveEnd()
{
if (counter > 0)
{
Node prevNode = new Node();
Node cur = head;
while (cur.next != null)
{
prevNode = cur;
cur = cur.next;
}
prevNode.next = null;
}
else
{
Console.WriteLine("No element exist in this linked list.");
}
}
public void Display()
{
Console.Write("Head ->");
Node curr = head;
while (curr.next != null)
{
curr = curr.next;
Console.WriteLine(curr.data.ToString());
}
}
public class Node
{
public object data;
public Node next;
}
static void Main(string[] args)
{
Program p = new Program();
p.AddEnd(2);
p.AddStart(1);
p.AddStart(0);
p.AddEnd(3);
p.Display();
p.RemoveStart();
Console.WriteLine("Removed node from Start");
p.Display();
Console.WriteLine("Removed node from End");
p.RemoveEnd();
p.Display();
Console.ReadKey();
}
}
}

The selected answer doesn't have an iterator; it is more basic, but perhaps not as useful.
Here is one with an iterator/enumerator. My implementation is based on Sedgewick's bag; see http://algs4.cs.princeton.edu/13stacks/Bag.java.html
void Main()
{
var b = new Bag<string>();
b.Add("bike");
b.Add("erasmus");
b.Add("kumquat");
b.Add("beaver");
b.Add("racecar");
b.Add("barnacle");
foreach (var thing in b)
{
Console.WriteLine(thing);
}
}
// Define other methods and classes here
public class Bag<T> : IEnumerable<T>
{
public Node<T> first;// first node in list
public class Node<T>
{
public T item;
public Node<T> next;
public Node(T item)
{
this.item = item;
}
}
public void Add(T item)
{
Node<T> oldFirst = first;
first = new Node<T>(item);
first.next = oldFirst;
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public IEnumerator<T> GetEnumerator()
{
return new BagEnumerator<T>(this);
}
public class BagEnumerator<V> : IEnumerator<T>
{
private Node<T> _head;
private Bag<T> _bag;
private Node<T> _curNode;
public BagEnumerator(Bag<T> bag)
{
_bag = bag;
_head = bag.first;
_curNode = default(Node<T>);
}
public T Current
{
get { return _curNode.item; }
}
object IEnumerator.Current
{
get { return Current; }
}
public bool MoveNext()
{
if (_curNode == null)
{
_curNode = _head;
if (_curNode == null)
return false;
return true;
}
if (_curNode.next == null)
return false;
else
{
_curNode = _curNode.next;
return true;
}
}
public void Reset()
{
_curNode = default(Node<T>); ;
}
public void Dispose()
{
}
}
}

I've created the following LinkedList code with many features. It is available for public under the CodeBase github public repo.
Classes:
Node and LinkedList
Getters and Setters: First and Last
Functions:
AddFirst(data), AddFirst(node), AddLast(data), RemoveLast(), AddAfter(node, data), RemoveBefore(node), Find(node), Remove(foundNode), Print(LinkedList)
using System;
using System.Collections.Generic;
namespace Codebase
{
public class Node
{
public object Data { get; set; }
public Node Next { get; set; }
public Node()
{
}
public Node(object Data, Node Next = null)
{
this.Data = Data;
this.Next = Next;
}
}
public class LinkedList
{
private Node Head;
public Node First
{
get => Head;
set
{
First.Data = value.Data;
First.Next = value.Next;
}
}
public Node Last
{
get
{
Node p = Head;
//Based partially on https://en.wikipedia.org/wiki/Linked_list
while (p.Next != null)
p = p.Next; //traverse the list until p is the last node.The last node always points to NULL.
return p;
}
set
{
Last.Data = value.Data;
Last.Next = value.Next;
}
}
public void AddFirst(Object data, bool verbose = true)
{
Head = new Node(data, Head);
if (verbose) Print();
}
public void AddFirst(Node node, bool verbose = true)
{
node.Next = Head;
Head = node;
if (verbose) Print();
}
public void AddLast(Object data, bool Verbose = true)
{
Last.Next = new Node(data);
if (Verbose) Print();
}
public Node RemoveFirst(bool verbose = true)
{
Node temp = First;
Head = First.Next;
if (verbose) Print();
return temp;
}
public Node RemoveLast(bool verbose = true)
{
Node p = Head;
Node temp = Last;
while (p.Next != temp)
p = p.Next;
p.Next = null;
if (verbose) Print();
return temp;
}
public void AddAfter(Node node, object data, bool verbose = true)
{
Node temp = new Node(data);
temp.Next = node.Next;
node.Next = temp;
if (verbose) Print();
}
public void AddBefore(Node node, object data, bool verbose = true)
{
Node temp = new Node(data);
Node p = Head;
while (p.Next != node) //Finding the node before
{
p = p.Next;
}
temp.Next = p.Next; //same as = node
p.Next = temp;
if (verbose) Print();
}
public Node Find(object data)
{
Node p = Head;
while (p != null)
{
if (p.Data == data)
return p;
p = p.Next;
}
return null;
}
public void Remove(Node node, bool verbose = true)
{
Node p = Head;
while (p.Next != node)
{
p = p.Next;
}
p.Next = node.Next;
if (verbose) Print();
}
public void Print()
{
Node p = Head;
while (p != null) //LinkedList iterator
{
Console.Write(p.Data + " ");
p = p.Next; //traverse the list until p is the last node.The last node always points to NULL.
}
Console.WriteLine();
}
}
}
Using #yogihosting answer when she used the Microsoft built-in LinkedList and LinkedListNode to answer the question, you can achieve the same results:
using System;
using System.Collections.Generic;
using Codebase;
namespace Cmd
{
static class Program
{
static void Main(string[] args)
{
var tune = new LinkedList(); //Using custom code instead of the built-in LinkedList<T>
tune.AddFirst("do"); // do
tune.AddLast("so"); // do - so
tune.AddAfter(tune.First, "re"); // do - re- so
tune.AddAfter(tune.First.Next, "mi"); // do - re - mi- so
tune.AddBefore(tune.Last, "fa"); // do - re - mi - fa- so
tune.RemoveFirst(); // re - mi - fa - so
tune.RemoveLast(); // re - mi - fa
Node miNode = tune.Find("mi"); //Using custom code instead of the built in LinkedListNode
tune.Remove(miNode); // re - fa
tune.AddFirst(miNode); // mi- re - fa
}
}

I have a doubly Linked List which can be used as a stack or a queue. If you look at the code and think about what it does and how it does it I bet you will understand everything about it. I am sorry but somehow I couldn't pate the full code here so I here is the link for the linkedlist(also I got the binary tree in the solution): https://github.com/szabeast/LinkedList_and_BinaryTree

A linked list is a node-based data structure. Each node designed with two portions (Data & Node Reference).Actually, data is always stored in Data portion (Maybe primitive data types eg Int, Float .etc or we can store user-defined data type also eg. Object reference) and similarly Node Reference should also contain the reference to next node, if there is no next node then the chain will end.
This chain will continue up to any node doesn't have a reference point to the next node.
Please find the source code from my tech blog - http://www.algonuts.info/linked-list-program-in-java.html
package info.algonuts;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
class LLNode {
int nodeValue;
LLNode childNode;
public LLNode(int nodeValue) {
this.nodeValue = nodeValue;
this.childNode = null;
}
}
class LLCompute {
private static LLNode temp;
private static LLNode previousNode;
private static LLNode newNode;
private static LLNode headNode;
public static void add(int nodeValue) {
newNode = new LLNode(nodeValue);
temp = headNode;
previousNode = temp;
if(temp != null)
{ compute(); }
else
{ headNode = newNode; } //Set headNode
}
private static void compute() {
if(newNode.nodeValue < temp.nodeValue) { //Sorting - Ascending Order
newNode.childNode = temp;
if(temp == headNode)
{ headNode = newNode; }
else if(previousNode != null)
{ previousNode.childNode = newNode; }
}
else
{
if(temp.childNode == null)
{ temp.childNode = newNode; }
else
{
previousNode = temp;
temp = temp.childNode;
compute();
}
}
}
public static void display() {
temp = headNode;
while(temp != null) {
System.out.print(temp.nodeValue+" ");
temp = temp.childNode;
}
}
}
public class LinkedList {
//Entry Point
public static void main(String[] args) {
//First Set Input Values
List <Integer> firstIntList = new ArrayList <Integer>(Arrays.asList(50,20,59,78,90,3,20,40,98));
Iterator<Integer> ptr = firstIntList.iterator();
while(ptr.hasNext())
{ LLCompute.add(ptr.next()); }
System.out.println("Sort with first Set Values");
LLCompute.display();
System.out.println("\n");
//Second Set Input Values
List <Integer> secondIntList = new ArrayList <Integer>(Arrays.asList(1,5,8,100,91));
ptr = secondIntList.iterator();
while(ptr.hasNext())
{ LLCompute.add(ptr.next()); }
System.out.println("Sort with first & Second Set Values");
LLCompute.display();
System.out.println();
}
}

Develop Reference

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

Reversing single linked list in C# - c#

Node p = root, n = null; while (p != null) { Node tmp = p.next; p.next = n; n = p; p = tmp; } root = n;

You don't need to make a copy. Some pseudo code: prev = null; current = head; next = current->next; (while next != null) current->next=prev prev=current current=next next=current->next

This performed pretty well on Leetcode. public ListNode ReverseList(ListNode head) { ListNode previous = null; ListNode current = head; while(current != null) { ListNode nextTemp = current.next; current.next = previous; previous = current; current = nextTemp; } return previous; }

public Node ReverseList(Node cur, Node prev) { if (cur == null) // if list is null return cur; Node n = cur.NextNode; cur.NextNode = prev; return (n == null) ? cur : ReverseList(n, cur); }

Complexity O(n+m). Assuming head is the start node: List<Node>Nodes = new List<Node>(); Node traverse= root; while(traverse!=null) { Nodes.Add(traverse); traverse = traverse.Next; } int i = Nodes.Count - 1; root = Nodes[i]; for(; i>0; i--) { Nodes[i].Next = Nodes[i-1]; } Nodes[0].Next=null;

In case you want a ready-made efficient implementation, I created an alternative to LinkedList that supports enumeration and reverse operations. https://github.com/NetFabric/NetFabric.DoubleLinkedList

public class Node<T> { public T Value { get; set; } public Node<T> Next { get; set; } } public static Node<T> Reverse<T>(Node<T> head) { Node<T> tail = null; while(head!=null) { var node = new Node<T> { Value = head.Value, Next = tail }; tail = node; head = head.Next; } return tail; }

The definition of ref is unnecessary because if you make the node as a reference type, it is OK to do: public static void Reverse(Node root) Also, the beauty of the interview question is less consumption of memory and in place reversal. Maybe a recursive way of doing it is also asked.

Related

Rotate Doubly Linked List

LinkedList Implementation Bug

Remove First from linked List

Breadth-first traversal

Creating a very simple linked list

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