C Program for Iterative Merge Sort

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Following is a typical recursive implementation of Merge Sort that uses last element as pivot.

C

/* Recursive C program for merge sort */
#include <stdio.h>  
#include <stdlib.h>  
  
/* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */
void merge(int arr[], int l, int m, int r);  
  
/* l is for left index and r is right index of the sub-array  
of arr to be sorted */
void mergeSort(int arr[], int l, int r)  
{  
 if (l < r) {  
  int m = l + (r - l) / 2; // Same as (l+r)/2 but avoids overflow for large l & h  
  mergeSort(arr, l, m);  
  mergeSort(arr, m + 1, r);  
  merge(arr, l, m, r);  
 }  
}  
  
/* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */
void merge(int arr[], int l, int m, int r)  
{  
 int i, j, k;  
 int n1 = m - l + 1;  
 int n2 = r - m;  
  
 /* create temp arrays */
 int L[n1], R[n2];  
  
 /* Copy data to temp arrays L[] and R[] */
 for (i = 0; i < n1; i++)  
  L[i] = arr[l + i];  
 for (j = 0; j < n2; j++)  
  R[j] = arr[m + 1 + j];  
  
 /* Merge the temp arrays back into arr[l..r]*/
 i = 0;  
 j = 0;  
 k = l;  
 while (i < n1 && j < n2) {  
  if (L[i] <= R[j]) {  
   arr[k] = L[i];  
   i++;  
  }  
  else {  
   arr[k] = R[j];  
   j++;  
  }  
  k++;  
 }  
  
 /* Copy the remaining elements of L[], if there are any */
 while (i < n1) {  
  arr[k] = L[i];  
  i++;  
  k++;  
 }  
  
 /* Copy the remaining elements of R[], if there are any */
 while (j < n2) {  
  arr[k] = R[j];  
  j++;  
  k++;  
 }  
}  
  
/* Function to print an array */
void printArray(int A[], int size)  
{  
 int i;  
 for (i = 0; i < size; i++)  
  printf("%d ", A[i]);  
 printf("\n");  
}  
  
/* Driver program to test above functions */
int main()  
{  
 int arr[] = { 12, 11, 13, 5, 6, 7 };  
 int arr_size = sizeof(arr) / sizeof(arr[0]);  
  
 printf("Given array is \n");  
 printArray(arr, arr_size);  
  
 mergeSort(arr, 0, arr_size - 1);  
  
 printf("\nSorted array is \n");  
 printArray(arr, arr_size);  
 return 0;  
}  

Output:

Given array is 
12 11 13 5 6 7 

Sorted array is 
5 6 7 11 12 13

Time Complexity: O(n*log(n))
Auxiliary Space: O(n)

Please refer complete article on Iterative Merge Sort for more details!

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