# C# - Sorting Algorithm - Merge Sort Iterative

We often using sorting algorithm to sort numbers and strings. Also we have many sorting algorithms. I have explained here on how merge sort algorithm works in iterative mode.

The iteration approach requires stacking of the beg(left), end(right) positions that are used in recursion. I have used the List to store the values and made sure the loop is getting repeated until List is empty. For DoMerger, we need three arguments - start, mid and right. I have used another List to store these values and then once all the index positions are calculated, then merely apply the DoMerger on these indexes.

The complete program and test run output are given below:

## Source Code

using System;

using System.Collections.Generic;

using System.Text;

namespace CSharpSort

{

class Program

{

static public void DoMerge(int [] numbers, int left, int mid, int right)

{

int [] temp = new int;

int i, left_end, num_elements, tmp_pos;

left_end = (mid - 1);

tmp_pos = left;

num_elements = (right - left + 1);

while ((left <= left_end) && (mid <= right))

{

if (numbers[left] <= numbers[mid])

temp[tmp_pos++] = numbers[left++];

else

temp[tmp_pos++] = numbers[mid++];

}

while (left <= left_end)

temp[tmp_pos++] = numbers[left++];

while (mid <= right)

temp[tmp_pos++] = numbers[mid++];

for (i = 0; i < num_elements; i++)

{

numbers[right] = temp[right];

right--;

}

}

struct MergePosInfo

{

public int left;

public int mid;

public int right;

};

static public void MergeSort_Iterative(int [] numbers, int left, int right)

{

int mid;

if (right <= left)

return;

List<MergePosInfo> list1 = new List<MergePosInfo>();

List<MergePosInfo> list2 = new List<MergePosInfo>();

MergePosInfo info;

info.left = left;

info.right = right;

info.mid = -1;

list1.Insert(list1.Count, info);

while(true)

{

if(list1.Count == 0)

break;

left = list1.left;

right = list1.right;

list1.RemoveAt(0);

mid = (right + left) / 2;

if(left < right)

{

MergePosInfo info2;

info2.left = left;

info2.right = right;

info2.mid = mid + 1;

list2.Insert(list2.Count, info2);

info.left = left;

info.right = mid;

list1.Insert(list1.Count, info);

info.left = mid + 1;

info.right = right;

list1.Insert(list1.Count, info);

}

}

for (int i = 0; i < list2.Count; i++)

{

DoMerge(numbers, list2[i].left, list2.mid, list2.right);

}

}

static void Main(string[] args)

{

int[] numbers = { 3, 8, 7, 5, 2, 1, 9, 6, 4 };

int len = 9;

Console.WriteLine("MergeSort By Iterative Method");

MergeSort_Iterative(numbers, 0, len - 1);

for (int i = 0; i < 9; i++)

Console.WriteLine(numbers[i]);

}

}

}

## Output

MergeSort By Iterative Method

1

2

3

4

5

6

7

8

9

Press any key to continue . . .