Develop Reference

No Output for MergeSort Algorithm c#

In my project I've implemented MergeSort, bubble sort, and sequential search algorithms, however the Merge sort is not giving any output to the console, while the others work. I've tried debugging with no real luck.
public static void mergeSort(int[] a)
{
int inputLength = a.Length;
//sets the middle index to the total length divided by 2
int midIndex = a.Length / 2;
//sets the last index to the length minus one (minus one included so
an out of bounds exception is avoided
int endIndex = a.Length - 1;
//left side set to the middle index size
int[] leftArray = new int[midIndex];
//right side set to the total length minus the middle length
int[] rightArray = new int[inputLength - midIndex];
//looping from zero to middle of the array
for (int i = 0; i < midIndex; i++)
{
leftArray[i] = a[i];
}
//looping from the middle to the end of the array
for(int i = midIndex; i < inputLength; i++)
{
rightArray[i - midIndex] = a[i];
}
//recursively called the method to sort these two sides
mergeSort(leftArray);
mergeSort(rightArray);
//this calls the merge method to put the two halves together
merge(a, leftArray, rightArray);
}
private static void merge(int[] a, int[] leftHalf, int[] rightHalf)
{
int leftSize = leftHalf.Length;
int rightSize = rightHalf.Length;
int i = 0, j = 0, k = 0;
//loops until no more elements in left or right array
while(i < leftSize && j < rightSize)
{
if(leftHalf[i] <= rightHalf[j])
{
//sets the element at iteration k to the elements at i in the
left half if
//it is smaller than the right half
a[k] = leftHalf[i];
i++;
}
else
{
//if the right half is smaller, set element at iteration k
equal to the
//element at index j of the right half
a[k] = rightHalf[j];
j++;
}
k++;//iterate K
}
//these account for leftover elements after the above while loop.
while (i < leftSize)
{
a[k] = leftHalf[i];
i++;
k++;
}
while (j < rightSize)
{
a[k] = rightHalf[j];
j++;
k++;
}
}
My main method is here:
static void Main(string[] args)
{
try{
TextFileReader reader = new TextFileReader();
int[] numberArray = reader.ReadFile("numbers.txt");
//printArray(numberArray);
Sorts sorts = new Sorts();
//sorts.bubbleSort(numberArray);
//printArray(numberArray);
//sorts.selectionSort(numberArray);
Searches searches = new Searches();
//searches.SequentialSearch(numberArray, 897);
//searches.binarySearch(numberArray, 9992);
//Console.WriteLine("\n\nArray length: " + numberArray.Length);
mergeSort(numberArray);
printArray(numberArray);
}
catch(IOException ex)
{
Console.WriteLine("IO Exception Found.");
}
}
public static void printArray(int[] numberArray)
{
foreach(int i in numberArray)
{
Console.WriteLine(i);
}
}
}
}
This is driving me crazy because the other algorithms are working and outputting correctly, but when the MergeSort is ran it gives no exceptions or errors.

returns the smallest positive integer (greater than 0) that does not occur in Array

I have the following question:-
Write a function:
class Solution { public int solution(int[] A); }
that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.
For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.
Given A = [1, 2, 3], the function should return 4.
Given A = [−1, −3], the function should return 1.
Write an efficient algorithm for the following assumptions:
N is an integer within the range [1..100,000];
each element of array A is an integer within the range [−1,000,000..1,000,000].
now i tried this code:-
using System;
// you can also use other imports, for example:
// using System.Collections.Generic;
// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");
class Solution
{
public int solution(int[] A)
{
// write your code in C# 6.0 with .NET 4.5 (Mono)
int n = 1;
Array.Sort(A);
for (int i = 1; i <= 100000; i++)
{
for (int i2 = 0; i2 <= A.Length - 1; i2++)
{
if (A[i2] == i)
{
n = A[i2] + 1;
break;
}
}
}
return n;
}
}
where my code worked well for these test data:-
A = [1, 2, 3]
A = [−1, −3]
while failed for this one:-
A = [1, 3, 6, 4, 1, 2] where it return 7 instead of 5.
any advice why my code failed on the 3rd test?
Thanks

using System.Linq;
int smallestNumber = Enumerable.Range(1, 100000).Except(A).Min();

I would use following approach that uses a HashSet<int> to check if a given integer is missing:
public static int? SmallestMissing(int[] A, int rangeStart = 1, int rangeEnd = 100_000)
{
HashSet<int> hs = new HashSet<int>(A);
for (int i = rangeStart; i <= rangeEnd; i++)
if(!hs.Contains(i)) return i;
return null;
}
A HashSet is a collection if unique values and it's very efficient in lookup items(complexity is O(1)). So you get a very readable and efficient algorithm at the cost of some memory.
Maybe you could optimize it by providing another algorithm in case the array is very large, you don't want to risk an OutOfMemoryException:
public static int? SmallestMissing(int[] A, int rangeStart = 1, int rangeEnd = 100_000)
{
if(A.Length > 1_000_000)
{
Array.Sort(A);
for (int i = rangeStart; i <= rangeEnd; i++)
{
int index = Array.BinarySearch(A, i);
if(index < 0) return i;
}
return null;
}
HashSet<int> hs = new HashSet<int>(A);
for (int i = rangeStart; i <= rangeEnd; i++)
if(!hs.Contains(i)) return i;
return null;
}

If you're allowed to sort the array in-place, which means modifying the input parameter value, here's a simple linear probe for the missing value (on top of the sort of course).
Here's the pseudo-code:
Sort the array
Skip all negatives and 0's at the start
Loopify the following:
Expect 1, if not found at current location return 1
Skip all 1's
Expect 2, if not found at current location return 2
Skip all 2's
Expect 3, if not found at current location return 3
Skip all 3's
... and so on for 4, 5, 6, etc. until end of array
If we get here, return currently expected value which should've been at the end
Here's the code:
public static int FirstMissingValue(int[] input)
{
Array.Sort(input);
int index = 0;
// Skip negatives
while (index < input.Length && input[index] < 1)
index++;
int expected = 1;
while (index < input.Length)
{
if (input[index] > expected)
return expected;
// Skip number and all duplicates
while (index < input.Length && input[index] == expected)
index++;
expected++;
}
return expected;
}
Test-cases:
Console.WriteLine(FirstMissingValue(new[] { 1, 3, 6, 4, 1, 2 }));
Console.WriteLine(FirstMissingValue(new[] { 1, 2, 3 }));
Console.WriteLine(FirstMissingValue(new[] { -1, -3 }));
output:
5
4
1

Your alg won't work in case input array becomes like this: [1,2-1,1,3,5]. I did this based on your alg. Give it a try:
int[] a = new int[] { -1, -2};
IEnumerable<int> uniqueItems = a.Distinct<int>().Where(x => x > 0);
if (uniqueItems.Count() == 0)
{
Console.WriteLine("result: 1");
}
else
{
Array asList = uniqueItems.ToArray();
Array.Sort(asList);
for (int i = 1; i <= 100000; i++)
{
if ((int)asList.GetValue(i - 1) != i)
{
Console.WriteLine("result: " + i);
break;
}
}
}

you can try like this.
public static int solution(int[] A)
{
int smallest = -1;
Array.Sort(A);
if(A[0] > 1)
return 1;
for(int i = 0; i < A.Length; i++)
{
if(A.Length != i+1 && A[i] + 1 != A[i + 1] && A[i+1] > 0)
{
smallest = A[i]+1;
break;
}
else if(A[i] > 0 && A.Length == i+1)
{
smallest = A[i] + 1;
}
}
return smallest > 0 ? smallest:1;
}

Here's the approach that uses O(N) partitioning followed by an O(N) search. This approach does not use any additional storage, but it DOES change the contents of the array.
This code was converted from here. Also see this article.
I've added comments to try to explain how the second stage findSmallestMissing() works. I've not commented the partitioning method, since that's just a variant of a standard partition as might be used in a QuickSort algorithm.
static class Program
{
public static void Main()
{
Console.WriteLine(FindSmallestMissing(1, 3, 6, 4, 1, 2));
Console.WriteLine(FindSmallestMissing(1, 2, 3));
Console.WriteLine(FindSmallestMissing(-1, -3));
}
public static int FindSmallestMissing(params int[] array)
{
return findSmallestMissing(array, partition(array));
}
// Places all the values > 0 before any values <= 0,
// and returns the index of the first value <= 0.
// The values are unordered.
static int partition(int[] arr)
{
void swap(int x, int y)
{
var temp = arr[x];
arr[x] = arr[y];
arr[y] = temp;
}
int pIndex = 0; // Index of pivot.
for (int i = 0; i < arr.Length; i++)
{
if (arr[i] > 0) // pivot is 0, hence "> 0"
swap(i, pIndex++);
}
return pIndex;
}
// This is the clever bit.
// We will use the +ve values in the array as flags to indicate that the number equal to that index is
// present in the array, by making the value negative if it is found in the array.
// This way we can store both the original number AND whether or not the number equal to that index is present
// in a single value.
//
// Given n numbers that are all > 0, find the smallest missing number as follows:
//
// For each array index i in (0..n):
// val = |arr[i]| - 1; // Subtract 1 so val will be between 0 and max +ve value in original array.
// if (val is in range) // If val beyond the end of the array we can ignore it
// and arr[val] is non-negative // If already negative, no need to make it negative.
// make arr[val] negative
//
// After that stage, we just need to find the first positive number in the array, which indicates that
// the number equal to that index + 1 is missing.
// n = number of values at the start of the array that are > 0
static int findSmallestMissing(int[] arr, int n)
{
for (int i = 0; i < n; i++)
{
int val = Math.Abs(arr[i]) - 1;
if (val < n && arr[val] >= 0)
arr[val] = -arr[val];
}
for (int i = 0; i < n; i++)
{
if (arr[i] > 0) // Missing number found.
return i + 1;
}
return n + 1; // No missing number found.
}
}

class Program
{
static void Main(string[] args)
{
int [] A = new int[] {1, 2, 3};
int n = 0;
bool found = false;
Array.Sort(A);
for (int i = 1; i <= 100000; i++) {
for (int x = 0; x <= A.Length - 1; x++) {
int next = (x + 1) < A.Length ? (x + 1): x;
if (A[x] > 0 && (A[next] - A[x]) > 0) {
n = A[x] + 1;
found = true;
break;
}
}
if(found) {
break;
}
}
Console.WriteLine("Smallest number: " + n);
}
}

int smallestNumber=Enumerable.Range(1,(int.Parse(A.Length.ToString())+1)).Except(A).Min();
Array.Sort(A);
for (int number = 1; number <= 100000; number++)
{
for (int num = number; i2 <= A.Length - 1; num++)
{
if (A[num] == number)
{
smallestNumber = A[num] + 1;
break;
}
}
}
return smallestNumber;
}

The easiest one :)
class Solution
{
public int solution(int[] array)
{
int[] onlyPositiveArray = array.Where(a => a > 0).OrderBy(a => a).Distinct().ToArray();
int smallestNumber = 1;
foreach (var number in onlyPositiveArray)
{
if (smallestNumber != number)
{
break;
}
smallestNumber ++;
}
if (!onlyPositiveArray.Contains(smallestNumber ))
{
return smallestNumber;
}
else
{
return smallestNumber + 1;
}
}
}

PHP Solution:
function solution($A) {
// write your code in PHP7.0
// sort array
sort($A);
// get the first
$smallest = $A[0];
// write while
while( in_array(($smallest),$A) || (($smallest) < 1 ) )
{
$smallest++;
}
return $smallest;
}

My solution, also if someone could test how performant it is?
public int solution(int[] N) {
if (N.Length == 0)
return 1;
else if (N.Length == 1)
return N[0] >= 0 ? N[0] + 1 : 1;
Array.Sort(N);
int min = Array.Find(N, IsUnderZero);
if (min ==
default)
return 1;
HashSet < int > hashSet = new HashSet < int > (N);
int max = N[N.Length - 1];
for (int i = min + 1; i <= max + 1; i++) {
if (!hashSet.Contains(i) && i > 0)
return i;
}
return max + 1;
bool IsUnderZero(int i) => i <= 0;
}

Try the below:
public static int MinIntegerGreaterThanZeroInArray(int[] A)
{
int minInt;
if (A.Length > 0)
{
Array.Sort(A);
for (minInt = 1; minInt <= A.Length; minInt++)
{
int index = Array.BinarySearch(A, minInt);
if (index < 0) return minInt;
}
return minInt;
}
//Array is empty.
throw new InvalidOperationException();
}

public static int Smallest(int[] A)
{
int maxPositiveInt = 1;
HashSet<int> NumDic = new HashSet<int>();
for (int i = 0; i < A.Length; i++)
{
if (A[i] <= 0)
{
continue;
}
if (!NumDic.Contains(A[i]))
{
NumDic.Add(A[i]);
}
maxPositiveInt = Math.Max(A[i], maxPositiveInt);
}
//All numbers are negative
if (NumDic.Count == 0)
{
return 1;
}
int smallestinteger = 1;
for (int i = 0; i < A.Length; i++)
{
if (A[i] <= 0)
{
continue;
}
if (!NumDic.Contains(smallestinteger))
{
return smallestinteger;
}
else
{
smallestinteger++;
}
}
return maxPositiveInt + 1;
}

static void Main(string[] args)
{
Console.WriteLine(solution(new int[]{1, 3, 6, 4, 1, 2}));
}
public static int solution(int[] A)
{
Array.Sort(A);
int smallest = A[0];
while (A.Contains(smallest+1)|| (smallest+1)<1)
{
smallest++;
}
return smallest +1;
}

Solving with only loop

The number 124 has the property that it is the smallest number whose first three multiples contain the digit 2. Observe that
124*1 = 124, 124*2 = 248, 124*3 = 372 and that 124, 248 and 372 each contain the digit 2. It is possible to generalize this property to be the smallest number whose first n multiples each contain the digit 2. Write a function named smallest(n) that returns the smallest number whose first n multiples contain the digit 2. Hint: use modulo base 10 arithmetic to examine digits.
Its signature is
int smallest(int n)
Examples
If n is return because
4 624 because the first four multiples of 624 are 624, 1248, 1872, 2496 and they all contain the
digit 2. Furthermore 624 is the smallest number whose first four multiples contain the digit 2.
5 624 because the first five multiples of 624 are 624, 1248, 1872, 2496, 3120. Note that 624 is also
the smallest number whose first 4 multiples contain the digit 2.
6 642 because the first five multiples of 642 are 642, 1284, 1926, 2568, 3210, 3852
7 4062 because the first five multiples of 4062 are 4062, 8124, 12186, 16248, 20310, 24372, 28434.
Note that it is okay for one of the multiples to contain the digit 2 more than once (e.g., 24372).
I tried to solve this by this way
//Its a incomplete code
public static int smallest(int n)
{
int i = 1;
for (; ; )
{
int temp = 0;
int myNum = 0;
for (int j = 1; j <= n; j++)
{
myNum = i * j;
//check for condition
}
//if condition ture break
}
}
But I am stick to the problem is I cannot create hard coded n times variable.. Can you help me proceed that?
You may assume that such a number is computable on a 32 bit machine, i.e, you do not have to detect integer overflow in your answer.

using System;
using System.Collections.Generic;
namespace firstconsoleproject
{
class MainClass
{
public static void Main (string[] args)
{
int first=4;
int c=0;
int ax;
int ai;
Console.WriteLine ("please enter n");
ax = Convert.ToInt32( Console.ReadLine());
for (int i=11 ; ax>0 ;)
{ if (first==1)
{
c = ax+1;
i++;
}
c--;
ai=i*c;
for (int ten=10 ; ; )
{
if(ai%ten==2)
{
first=0;
break;
}else if (ai==0)
{
first=1;
break;
}
ai/=10;
}
if (c==0){Console.WriteLine("number is "+i);break;}
}Console.ReadKey ();
}
}
}

// Function smallest n
public int smallest(int a)
{
int temp = 0, holder = 0, k = 0;
if (a <= 0) return 0;
else
{
for (int i = 100; i < Int16.MaxValue; i++)
{
int count = 0;
k = 0;
int[] array = new int[a];
for (int j = 1; j < 9; j++)
{
holder = i * j;
temp = holder;
while (temp > 0)
{
int rem = temp % 10;
if (rem == 2)
{
count++;
if (k < a)
{
array[k] = j;
k++;
break;
}
}
temp /= 10;
}
if (count == a)
{
int countTemp = 0;
for (int h = 0; h < a; h++)
{
if (h + 1 < a)
{
if (array[h + 1] == array[h] + 1 && array[0] == 1 && array[h] > 0)
{
countTemp++;
if (countTemp == a - 1)
return i;
}
}
}
}
}
}
}
return 0;
}

public static int smallest(int n)
{
int i = 1;
for (; ; )
{
int contain = 0;
int temp = 0;
int myNum = 0;
for (int j = 1; j <= n; j++)
{
myNum = i * j;
temp = myNum;
while (true)
{
if (temp % 10 == 2)
{
contain++;
break;
}
temp = temp / 10;
if (temp <= 0)
break;
}
}
if (contain == n)
break;
i++;
}
return i;
}

"myList.Count" is less then the amount of elements inside the list

I have a task to write a program that takes some numbers and step as input. Then it must make a sequence of binary representation of those numbers and destroy bits at positions 1, 1*step, 2*step, 3*step... Here is the code:
using System;
using System.Collections.Generic;
class BitKiller
{
static void Main()
{
int
amountNumbers = int.Parse(Console.ReadLine()),
step = int.Parse(Console.ReadLine()),
counter = 0,
number = 0
;
int[]
numBin= new int[8],
numbers = new int[amountNumbers]
;
var sequence = new List<int>();
for(int i = 0; i < amountNumbers; i++)
{
numbers[i] = int.Parse(Console.ReadLine());
numBin = ToBin(numbers[i]);
sequence.InsertRange(counter * 8, numBin);
foreach(int b in sequence)
{
Console.Write(b);
}
Console.WriteLine("");
counter++;
}
if(step == 1)
{
Console.WriteLine(0);
return;
}
for(int i = sequence.Count; i >= 0; i--)
{
if(i % step == 1)
{
sequence.RemoveAt(i);
}
}
Console.WriteLine("List count = {0}", sequence.Count);
if(sequence.Count % 8 != 0)
{
int padding = 8 - (sequence.Count % 8);
for(int i = 0; i < padding; i++)
{
sequence.Add(0);
}
}
foreach(int b in sequence)
{
Console.Write(b);
}
Console.WriteLine("");
for(int i = 7, power = 0, y = 0; y < sequence.Count; i--, y++, power++)
{
number = number + (sequence[i]) * ToPower(2, power);
if(i == 0)
{
Console.WriteLine("Result = {0}", number);
sequence.RemoveRange(0, 8);
foreach(int b in sequence)
{
Console.Write(b);
}
Console.WriteLine("");
number = 0;
i = 7;
y = 0;
power = 0;
}
}
}
static int[] ToBin(int number)
{
var binSequence = new int[8];
for(int i = 7; i >= 0; number /= 2, i--)
{
if(number % 2 == 0 || (number == 0 && i >= 0))
{
binSequence[i] = 0;
}
else
{
binSequence[i] = 1;
}
}
return binSequence;
}
static int ToPower(int number, int power)
{
int numberReturn = number;
if(power == 0)
{
return 1;
}
if(number == 1)
{
return number;
}
for(int i = 0; i < power - 1; i++)
{
numberReturn = numberReturn * number;
}
return numberReturn;
}
}
Now, there are a couple of extra print lines so you can see the binary numbers coming up as you input numbers. In short my program converts the numbers to lists containing only '1' and '0' and then removes values from this list according to my formula. My main question is why is:
sequence.Count
returning 22, when there are obviously 24 '1's inside the list. Test it with the following input: 3,19,255,255,255. The Result will be: 255, 254, 252, while the correct output would be 255, 255, 252.
It is happening, because of this code:
if(sequence.Count % 8 != 0)
{
int padding = 8 - (sequence.Count % 8);
for(int i = 0; i < padding; i++)
{
sequence.Add(0);
}
}
Because the sequence.Count is 22 ( why? ) the condition is true and the following for loop is replacing my last two '1's with 2 zeros. Which is causing the wrong output. So back to the point. Why is sequence.Count equal to 22, when there are 24 '1's in the list.
Sorry, if it is a bit long and confusing, but I posted the whole code, because I have no idea what and how could be interfering to cause this issue.

You are removing two items from the list in this code:
for(int i = sequence.Count; i >= 0; i--)
{
if(i % step == 1)
{
sequence.RemoveAt(i);
}
}
With the example input you gave, sequence.RemoveAt is being called when i == 20 and when i == 1. There were 24 items, then you removed 2 of them.

Duly noted: A whole day into programming affects my basic calculus. The list count and if conditions are both performing properly. After another hour of testing I realized that the problem was that I need to set both 'y' and 'i' to - 1 value, because they are incrementing instantly by 1 when they hit the for loop. Thanks for the tips.

Order an array in a specific order

I have this array of integers:-
int[] numbers = new int[] { 10, 20, 30, 40 };
I am trying to create an array which will have first element, last element, second element, second-last element and so on..
So, my resulting output will be:-
int[] result = {10,40,20,30};
This was my approach, in one loop start from first and go till the middle & in second loop start from last and get to the middle and select items accordingly, but I totally messed it up. Here is my attempted code:-
private static IEnumerable<int> OrderedArray(int[] numbers)
{
bool takeFirst = true;
if (takeFirst)
{
takeFirst = false;
for (int i = 0; i < numbers.Length / 2; i++)
{
yield return numbers[i];
}
}
else
{
takeFirst = true;
for (int j = numbers.Length; j < numbers.Length / 2; j--)
{
yield return numbers[j];
}
}
}
Need Help.

You might try this:
int[] result = numbers.Zip(numbers.Reverse(), (n1,n2) => new[] {n1, n2})
.SelectMany(x =>x)
.Take(numbers.Length)
.ToArray();
Explanation: This approach basically pairs up the elements of the original collection with the elements of its reverse ordered collection (using Zip). So you get a collection of pairs like [first, last], [second, second from last], etc.
It then flattens those collection of pairs into a single collection (using SelectMany). So the collection becomes [first, last, second, second from last,...].
Finally, we limit the number of elements to the length of the original array (n). Since we are iterating through twice as many elements (normal and reverse), it works out that iterating through n elements allow us to stop in the middle of the collection.
As a different approach, this is a modification on your existing method:
private static IEnumerable<int> OrderedArray(int[] numbers)
{
var count = (numbers.Length + 1) / 2;
for (int i = 0; i < count; i++)
{
yield return numbers[i];
int reverseIdx = numbers.Length - 1 - i;
if(i != reverseIdx)
yield return numbers[reverseIdx];
}
}

ok,
public static class Extensions
{
public static IEnumerable<T> EndToEnd<T>(this IReadOnlyList<T> source)
{
var length = source.Count;
var limit = length / 2;
for (var i = 0; i < limit; i++)
{
yield return source[i];
yield return source[length - i - 1];
}
if (length % 2 > 0)
{
yield return source[limit];
}
}
}
Which you could use like this,
var result = numbers.EndToEnd().ToArray();
more optimally,
public static class Extensions
{
public static IEnumerable<T> EndToEnd<T>(this IReadOnlyList<T> source)
{
var c = source.Count;
for (int i = 0, f = 0, l = c - 1; i < c; i++, f++, l--)
{
yield return source[f];
if (++i == c)
{
break;
}
yield return source[l];
}
}
}
no divide or modulus required.

With a simple for;
int len = numbers.Length;
int[] result = new int[len];
for (int i = 0, f = 0, l = len - 1; i < len; f++, l--)
{
result[i++] = numbers[f];
if (f != l)
result[i++] = numbers[l];
}

Based on Selman22's now deleted answer:
int[] numbers = new int[] { 10, 20, 30, 40 };
int[] result = numbers
.Select((x,idx) => idx % 2 == 0
? numbers[idx/2]
: numbers[numbers.Length - 1 -idx/2])
.ToArray();
result.Dump();
(The last line is LinqPad's way of outputting the results)
Or in less LINQy form as suggested by Jeppe Stig Nielsen
var result = new int[numbers.Length];
for (var idx = 0; idx < result.Length; idx++) {
result[idx] = idx % 2 == 0 ? numbers[idx/2] : numbers[numbers.Length - 1 -idx/2];
}
The principle is that you have two sequences, one for even elements (in the result) and one for odd. The even numbers count the first half of the array and the odds count the second half from the back.
The only modification to Selman's code is adding the /2 to the indexes to keep it counting one by one in the right half while the output index (which is what idx basically is in this case) counts on.

Came up with this
static void Main(string[] args)
{
List<int> numbers = new List<int>() { 10, 20, 30, 40, 50, 60, 70};
List<int> numbers2 = new List<int>();
int counter1 = 0;
int counter2 = numbers.Count - 1;
int remainder = numbers.Count % 2 == 0 ? 1: 0;
while (counter1-1 < counter2)
{
if (counter1 + counter2 % 2 == remainder)
{
numbers2.Add(numbers[counter1]);
counter1++;
}
else
{
numbers2.Add(numbers[counter2]);
counter2--;
}
}
string s = "";
for(int a = 0; a< numbers2.Count;a++)
s+=numbers2[a] + " ";
Console.Write(s);
Console.ReadLine();
}

This late answer steals a lot from the existing answers!
The idea is to allocate the entire result array at once (since its length is known). Then fill out all even-indexed members first, from one end of source. And finally fill out odd-numbered entries from the back end of source.
public static TElement[] EndToEnd<TElement>(this IReadOnlyList<TElement> source)
{
var count = source.Count;
var result = new TElement[count];
for (var i = 0; i < (count + 1) / 2; i++)
result[2 * i] = source[i];
for (var i = 1; i <= count / 2; i++)
result[2 * i - 1] = source[count - i];
return result;
}

Came up with this
public int[] OrderedArray(int[] numbers)
{
int[] final = new int[numbers.Length];
var limit=numbers.Length;
int last = numbers.Length - 1;
var finalCounter = 0;
for (int i = 0; finalCounter < numbers.Length; i++)
{
final[finalCounter] = numbers[i];
final[((finalCounter + 1) >= limit ? limit - 1 : (finalCounter + 1))] = numbers[last];
finalCounter += 2;
last--;
}
return final;
}