C Program for Iterative Merge Sort

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

/* 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

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

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