so in my application , I read some files into it and ask the user for a number , in these files there a lot of numbers and I am trying to find the nearest value when the number they enter is not in the file. So far I have as following
static int nearest(int close_num, int[] a)
{
foreach (int bob in a)
{
if ((close_num -= bob) <= 0)
return bob;
}
return -1;
}
Console.WriteLine("Enter a number to find out if is in the selected Net File: ");
int i3 = Convert.ToInt32(Console.ReadLine());
bool checker = false;
//Single nearest = 0;
//linear search#1
for (int i = 0; i < a.Length; i++)//looping through array
{
if(a[i] == i3)//checking to see the value is found in the array
{
Console.WriteLine("Value found and the position of it in the descending value of the selected Net File is: " + a[i]);
checker = true;
}
else
{
int found = nearest(i3,a);
Console.WriteLine("Cannot find this number in the Net File however here the closest number to that: " + found );
//Console.WriteLine("Cannot find this number in the Net File however here the closest number to that : " + nearest);
}
}
When a value that is in the file is entered the output is fine , but when it comes to the nearest value I cannot figure a way. I can't use this such as BinarySearchArray for this. a = the array whilst i3 is the value the user has entered. Would a binary search algorithm just be simpler for this?
Any help would be appreciated.
You need to make a pass over all the elements of the array, comparing each one in turn to find the smallest difference. At the same time, keep a note of the current nearest value.
There are many ways to do this; here's a fairly simple one:
static int nearest(int close_num, int[] a)
{
int result = -1;
long smallestDelta = long.MaxValue;
foreach (int bob in a)
{
long delta = (bob > close_num) ? (bob - close_num) : (close_num - bob);
if (delta < smallestDelta)
{
smallestDelta = delta;
result = bob;
}
}
return result;
}
Note that delta is calculated so that it is the absolute value of the difference.
Well, first we should define, what is nearest. Assuming that,
int nearest for given int number is the item of int[] a such that Math.Abs(nearest - number) is the smallest possible value
we can put it as
static int nearest(int number, int[] a)
{
long diff = -1;
int result = 0;
foreach (int item in a)
{
// actual = Math.Abs((long)item - number);
long actual = (long)item - number;
if (actual < 0)
actual = -actual;
// if item is the very first value or better than result
if (diff < 0 || actual < diff) {
result = item;
diff = actual;
}
}
return result;
}
The only tricky part is long for diff: it may appear that item - number exceeds int range (and will either have IntegerOverflow exceprion thrown or *invalid answer), e.g.
int[] a = new int[] {int.MaxValue, int.MaxValue - 1};
Console.Write(nearest(int.MinValue, a));
Note, that expected result is 2147483646, not 2147483647
what about LINQ ?
var nearestNumber = a.OrderBy(x => Math.Abs(x - i3)).First();
Just iterate through massive and find the minimal delta between close_num and array members
static int nearest(int close_num, int[] a)
{
// initialize as big number, 1000 just an example
int min_delta=1000;
int result=-1;
foreach (int bob in a)
{
if (Math.Abs(bob-close_num) <= min_delta)
{
min_delta = bob-close_num;
result = bob;
}
}
return result;
}
Related
I have a textbox to write the position of an array and a textbox to write the value of that position. Every time I want to add a value and a position I click the button btnStoreValue
I created a function (CompareTwoNumbers) for another exercise that compares two numbers and returns the biggest
Using that function and avoiding the use of comparison characters like > and < I'm supposed to get the biggest value of the array
public partial class Form1 : ExerciseArray
{
int[] numbers = new int[10];
private int CompareTwoNumbers(int i, int j)
{
if (i < j)
{
return j;
}
return i;
}
private void btnBiggestValue_Click(object sender, EventArgs e)
{
//int n=1;
int counter = 0;
int highestPosition = CompareTwoNumbers(0, 1);
for(int i=0; i<10; i++){
//int j = CompareTwoNumbers(numbers[i], numbers[i+1])
//n = CompareTwoNumbers(numbers[n], numbers[i+1]
counter = CompareTwoNumbers(highestPosition, i);
}
txtBiggestValuePosition.Text= n.ToString();
txtBiggestValue.Text=numbers[n].ToString();
}
I've tried multiple things, using multiple variables, I tried to write it on paper to try to understand things better and I'm stuck. I don't know how is it possible to find that value using the function I created on the previous exercise (assuming the function I created is correct)
So, the core part of your question is that you want to know how to find the biggest number in an array using your helper function CompareTwoNumbers and then figure out what the value and position of the biggest number is.
Based on my understanding above, you have the framework almost set up correctly.
First off, CompareTwoNumbers should be updated to return a bool. Doing this will let you conditionally update your variables holding the biggest number value and position.
private int CompareTwoNumbers(int i, int j)
{
if (i < j)
{
return true;
}
return false;
}
To know what the largest value in an (unsorted) array is, you will need to iterate through every value. While doing so, you need to keep track of the value and position of the biggest value, only updating it when a bigger value is found.
private void btnBiggestValue_Click(object sender, EventArgs e)
{
// Store the bigget number's index and value
// We start with the first index and corresponding
// value to give us a starting point.
int biggestNumberIndex = 0;
int biggestNumber = numbers[0];
// Iterate through the array of numbers to find
// the biggest number and its index
for(int i=0; i<10; i++)
{
// If the current number is larger than the
// currently stored biggest number...
if(CompareTwoNumbers(biggestNumber, numbers[i])
{
// ...then update the value and index with
// the new biggest number.
biggestNumber = number[i];
biggestNumberIndex = i;
}
}
// Finally, update the text fields with
// the correct biggest value and biggest
// value position.
txtBiggestValuePosition.Text= biggestNumberIndex.ToString();
txtBiggestValue.Text=numbers[biggestNumberIndex].ToString();
}
This uses a Tuple to give you both the max index and max value from the same method:
public (int, int) FindMaxValue(int[] items)
{
int maxValue = items[0];
int maxIndex = 0;
for(int i=1;i<items.Length;i++)
{
if (items[i] > maxValue)
{
maxValue = items[i];
maxIndex = i;
}
}
return (maxIndex, maxValue);
}
I've been going though www.testdome.com to test my skills and opened a list of public questions. One of the practice questions was:
Implement function CountNumbers that accepts a sorted array of
integers and counts the number of array elements that are less than
the parameter lessThan.
For example, SortedSearch.CountNumbers(new int[] { 1, 3, 5, 7 }, 4)
should return 2 because there are two array elements less than 4.
And my answer was:
using System;
public class SortedSearch
{
public static int CountNumbers(int[] sortedArray, int lessThan)
{
int count = 0;
int l = sortedArray.Length;
for (int i = 0; i < l; i++) {
if (sortedArray [i] < lessThan)
count++;
}
return count;
}
public static void Main(string[] args)
{
Console.WriteLine(SortedSearch.CountNumbers(new int[] { 1, 3, 5, 7 }, 4));
}
}
It seems that I've failed on two counts:
Performance test when sortedArray contains lessThan: Time limit exceeded
and
Performance test when sortedArray doesn't contain lessThan: Time limit exceeded
To be honest I'm not sure what to optimize there? Maybe I'm using a wrong method and there is a similar way to speed up the calculation?
If someone could point out my mistake or explain what I'm going wrong, I'd really appreciate it!
Because the array is sorted, you can stop counting as soon as you reach or exceed the lessThan parameter.
else break would probably do it.
Does it have to be really a loop? You could do Lambda exp for that
public static int CountNumbers(int[] sortedArray, int lessThan)
{
return sortedArray.ToList().Where(x=>x < lessThan).Count();
}
Harold's answer and approach is spot on.
Find below another code sample in case you're practicing for technical interviews. It handles cases when the array is null or empty, when lessThan is presented in the array (including duplicates), etc.
private static int CountNumbers(int[] sortedArray, int lessThan)
{
if (sortedArray == null)
{
throw new ArgumentNullException("Sorted array cannot be null.");
}
if (sortedArray.Length == 0)
{
throw new ArgumentException("Sorted array cannot be empty.");
}
int start = 0;
int end = sortedArray.Length;
int middle = int.MinValue;
while (start < end)
{
middle = (start + end) / 2;
if (sortedArray[middle] == lessThan)
{
break; // Found the "lessThan" number in the array, we can stop and move left
}
else if (sortedArray[middle] < lessThan)
{
start = middle + 1;
}
else
{
end = middle - 1;
}
}
// Adjust the middle pointer based on the "current" and "lessThan" numbers in the sorted array
while (middle >= 0 && sortedArray[middle] >= lessThan)
{
middle--;
}
// +1 because middle is calculated through 0-based (e.g. start)
return middle + 1;
}
So I have a Json implimentation that reads characters, the names go into arrays then I use Array.BinarySearch to get the position of the element.
I'm researching how to impliment the Binary Search own my own. I'm having trouble seeing logically what to do with the string name that is entered for the search.
Instead of using Array.BinarySearch, I need a separate method with the algorithm.
Any advice / strategy? :)
example:
/* json array implimented, manu printed etc... before this point, */
static void FindCharacters(Characters[] characters)
{
Characters result = new Characters();
string userInput = Console.ReadLine();
string[] name = new string[10000];
Console.Write("Search Name : ");
string searchKeyword = Console.ReadLine();
if (userInput.ToLower() == "name")
{
name = characters.Select(m => m.Name).ToArray();
Array.Sort(name);
Sorting.Sort(characters, searchKeyword);
var tmp = BinarySearch(name, searchKeyword);
if (tmp < 0)
{
Console.WriteLine("No data found!");
return;
}
else
{
result = characters[tmp];
CharacterPrint(result);
}
//result = characters[tmp]; //Convert.ToInt32(tmp)
//CharacterPrint(result);
}
public static int BinarySearch(int[] name, int item)
{
int min = 0;
int N = name.Length;
int max = N - 1;
do
{
int mid = (min + max) / 2;
if (item > name[mid])
min = mid + 1;
else
max = mid - 1;
if (name[mid] == item)
return mid;
//if (min > max)
// break;
} while (min <= max);
return -1;
}
Your int solution will work perfectly fine for strings. In fact, by just tweaking a couple lines, it would work for any data type that implements IComparable:
public static int BinarySearch<T>(T[] name, T item)
where T : IComparable<T>
{
int min = 0;
int N = name.Length;
int max = N - 1;
do
{
int mid = (min + max) / 2;
int t = item.CompareTo(name[mid]); // Temp value holder
if (t > 0) // item > name[mid]
min = mid + 1;
else if (t < 0) // item < name[mid]
max = mid - 1;
else // item == name[mid]
return mid;
//if (min > max)
// break;
} while (min <= max);
return -1;
}
You can call it like this:
string[] names = // ...
string name = //...
// Explicit calling
int idx = BinarySearch<string>(names, name);
// Implicit calling
// The following option works because the C# compiler can tell you are
// using two values of type string and inserts the correct generic
// type for you
int idx = BinarySearch(names, name);
You can see the changes made above reflect how to replace the default comparison operators (i.e. "<", ">", "==") with their CompareTo equivolents. The extra variable t is there to avoid redundantly calling CompareTo on the objects twice.
The way that CompareTo works is that it takes the calling object and compares it with the passed object. If the passed object would appear before the calling object in a sorted list, the method returns -1. If it would appear after, it returns 1. If they are the same, it returns 0.
See the following example for an illustration of this:
// The following values are compared based on standard lexical alphabetical order
a.CompareTo(b); // "b" would appear after "a", so this returns 1
c.CompareTo(b); // "b" would appear before "c", so this returns -1
b.CompareTo(b); // "b" and "b" are the same value, so this returns 0
Length = input Long(can be 2550, 2880, 2568, etc)
List<long> = {618, 350, 308, 300, 250, 232, 200, 128}
The program takes a long value, for that particular long value we have to find the possible combination from the above list which when added give me a input result(same value can be used twice). There can be a difference of +/- 30.
Largest numbers have to be used most.
Ex:Length = 868
For this combinations can be
Combination 1 = 618 + 250
Combination 2 = 308 + 232 + 200 +128
Correct Combination would be Combination 1
But there should also be different combinations.
public static void Main(string[] args)
{
//subtotal list
List<int> totals = new List<int>(new int[] { 618, 350, 308, 300, 250, 232, 200, 128 });
// get matches
List<int[]> results = KnapSack.MatchTotal(2682, totals);
// print results
foreach (var result in results)
{
Console.WriteLine(string.Join(",", result));
}
Console.WriteLine("Done.");
}
internal static List<int[]> MatchTotal(int theTotal, List<int> subTotals)
{
List<int[]> results = new List<int[]>();
while (subTotals.Contains(theTotal))
{
results.Add(new int[1] { theTotal });
subTotals.Remove(theTotal);
}
if (subTotals.Count == 0)
return results;
subTotals.Sort();
double mostNegativeNumber = subTotals[0];
if (mostNegativeNumber > 0)
mostNegativeNumber = 0;
if (mostNegativeNumber == 0)
subTotals.RemoveAll(d => d > theTotal);
for (int choose = 0; choose <= subTotals.Count; choose++)
{
IEnumerable<IEnumerable<int>> combos = Combination.Combinations(subTotals.AsEnumerable(), choose);
results.AddRange(from combo in combos where combo.Sum() == theTotal select combo.ToArray());
}
return results;
}
public static class Combination
{
public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements, int choose)
{
return choose == 0 ?
new[] { new T[0] } :
elements.SelectMany((element, i) =>
elements.Skip(i + 1).Combinations(choose - 1).Select(combo => (new[] { element }).Concat(combo)));
}
}
I Have used the above code, can it be more simplified, Again here also i get unique values. A value can be used any number of times. But the largest number has to be given the most priority.
I have a validation to check whether the total of the sum is greater than the input value. The logic fails even there..
The algorithm you have shown assumes that the list is sorted in ascending order. If not, then you shall first have to sort the list in O(nlogn) time and then execute the algorithm.
Also, it assumes that you are only considering combinations of pairs and you exit on the first match.
If you want to find all combinations, then instead of "break", just output the combination and increment startIndex or decrement endIndex.
Moreover, you should check for ranges (targetSum - 30 to targetSum + 30) rather than just the exact value because the problem says that a margin of error is allowed.
This is the best solution according to me because its complexity is O(nlogn + n) including the sorting.
V4 - Recursive Method, using Stack structure instead of stack frames on thread
It works (tested in VS), but there could be some bugs remaining.
static int Threshold = 30;
private static Stack<long> RecursiveMethod(long target)
{
Stack<long> Combination = new Stack<long>(establishedValues.Count); //Can grow bigger, as big as (target / min(establishedValues)) values
Stack<int> Index = new Stack<int>(establishedValues.Count); //Can grow bigger
int lowerBound = 0;
int dimensionIndex = lowerBound;
long fail = -1 * Threshold;
while (true)
{
long thisVal = establishedValues[dimensionIndex];
dimensionIndex++;
long afterApplied = target - thisVal;
if (afterApplied < fail)
lowerBound = dimensionIndex;
else
{
target = afterApplied;
Combination.Push(thisVal);
if (target <= Threshold)
return Combination;
Index.Push(dimensionIndex);
dimensionIndex = lowerBound;
}
if (dimensionIndex >= establishedValues.Count)
{
if (Index.Count == 0)
return null; //No possible combinations
dimensionIndex = Index.Pop();
lowerBound = dimensionIndex;
target += Combination.Pop();
}
}
}
Maybe V3 - Suggestion for Ordered solution trying every combination
Although this isn't chosen as the answer for the related question, I believe this is a good approach - https://stackoverflow.com/a/17258033/887092(, otherwise you could try the chosen answer (although the output for that is only 2 items in set being summed, rather than up to n items)) - it will enumerate every option including multiples of the same value. V2 works but would be slightly less efficient than an ordered solution, as the same failing-attempt will likely be attempted multiple times.
V2 - Random Selection - Will be able to reuse the same number twice
I'm a fan of using random for "intelligence", allowing the computer to brute force the solution. It's also easy to distribute - as there is no state dependence between two threads trying at the same time for example.
static int Threshold = 30;
public static List<long> RandomMethod(long Target)
{
List<long> Combinations = new List<long>();
Random rnd = new Random();
//Assuming establishedValues is sorted
int LowerBound = 0;
long runningSum = Target;
while (true)
{
int newLowerBound = FindLowerBound(LowerBound, runningSum);
if (newLowerBound == -1)
{
//No more beneficial values to work with, reset
runningSum = Target;
Combinations.Clear();
LowerBound = 0;
continue;
}
LowerBound = newLowerBound;
int rIndex = rnd.Next(LowerBound, establishedValues.Count);
long val = establishedValues[rIndex];
runningSum -= val;
Combinations.Add(val);
if (Math.Abs(runningSum) <= 30)
return Combinations;
}
}
static int FindLowerBound(int currentLowerBound, long runningSum)
{
//Adjust lower bound, so we're not randomly trying a number that's too high
for (int i = currentLowerBound; i < establishedValues.Count; i++)
{
//Factor in the threshold, because an end aggregate which exceeds by 20 is better than underperforming by 21.
if ((establishedValues[i] - Threshold) < runningSum)
{
return i;
}
}
return -1;
}
V1 - Ordered selection - Will not be able to reuse the same number twice
Add this very handy extension function (uses a binary algorithm to find all combinations):
//Make sure you put this in a static class inside System namespace
public static IEnumerable<List<T>> EachCombination<T>(this List<T> allValues)
{
var collection = new List<List<T>>();
for (int counter = 0; counter < (1 << allValues.Count); ++counter)
{
List<T> combination = new List<T>();
for (int i = 0; i < allValues.Count; ++i)
{
if ((counter & (1 << i)) == 0)
combination.Add(allValues[i]);
}
if (combination.Count == 0)
continue;
yield return combination;
}
}
Use the function
static List<long> establishedValues = new List<long>() {618, 350, 308, 300, 250, 232, 200, 128, 180, 118, 155};
//Return is a list of the values which sum to equal the target. Null if not found.
List<long> FindFirstCombination(long target)
{
foreach (var combination in establishedValues.EachCombination())
{
//if (combination.Sum() == target)
if (Math.Abs(combination.Sum() - target) <= 30) //Plus or minus tolerance for difference
return combination;
}
return null; //Or you could throw an exception
}
Test the solution
var target = 858;
var result = FindFirstCombination(target);
bool success = (result != null && result.Sum() == target);
//TODO: for loop with random selection of numbers from the establishedValues, Sum and test through FindFirstCombination
Basically comparing a string that is entered, and trying to get that position from the array.
If I initialize position to 0 then it returns the position zero of the array, if I initialize to 1 then it gives me the item in slot 1, so it's skipping the compare statement.
I also tried using (custStatus == cardStatus[i])
public static int discount(string []cardStatus, int []pDiscount, string custStatus)
{
int position= 0;
int discount;
for(int i = 0; i < 2; i++)
{
if (string.Equals(custStatus, cardStatus[i]))
position = i;
}
discount = pDiscount[position];
return discount;
}
With your code, there's no way to tell if position = 0 means custStatus was found in your cardStatus array or if no match was made at all and the default value is being used. I'd recommend either using a boolean matchFound variable or setting position = -1 and adding an extra if statement at the end either way. Either:
boolean matchFound = false;
...
if(matchFound)
{
discount = pDiscount[position];
}
or else
int position = -1;
...
if(position >= 0)
{
discount = pDiscount[position];
}
Give this a try:
public static int discount(string[] cardStatus, int[] pDiscount, string custStatus) {
var position = Array.IndexOf(cardStatus, custStatus);
return (position == -1) ? -1 : pDiscount[position];
}
public static int discount(string []cardStatus, int []pDiscount, string custStatus)
{
for(int i = 0; i < Math.Min(cardStatus.Length, pDiscount.Length); i++)
{
if (string.Equals(custStatus, cardStatus[i]))
{
return pDiscount[i];
}
}
return -1;
}
Don't be afraid to return directly from FOR-loop, it is old-school that teaches to have only one return point from method. You can have as many returns as it helps you to keep your code clean and easy to read.
And perhaps it would be better to use the following expression in for-loop as it will guard you from possible different lengths of arrays:
for (int i = 0; i < Math.Min(cardStatus.Length, pDiscount.Length; i++)
This looks ok, even though this is somewhat more straightforward:
for(int i = 0; i < cardStatus.Length; i++)
{
if (custStatus == cardStatus[i])
{
position = i;
break;
}
}
Given your question it appears to be the case that all cardStatus[i] match custStatus - did you check the input?
Also given your code what happens if there is no match? Currently you would return pDiscount[0] - that doesn't seem to be correct.