C Program for Iterative Merge Sort

Merge sort what is a sorting algorithm based on the divide and conquer technique. the time complexity of merge sort is O(n log n). The algorithm first divides the array into equal halves and then merges them in a certain manner.

Iterative merge sort

In iterative merge sort, we will divide the elements into equal halves using a recursive approach and then merge them back as a sorted array using the iterative approach.

Program for iterative Merge Sort

/* Recursive C program for merge sort */

Example

 Live Demo

#include<stdlib.h>
#include<stdio.h>
void merge(int arr[], int l, int m, int r) {
   int i, j, k;
   int n1 = m - l + 1;
   int n2 = r - m;
   int L[n1], R[n2];
   for (i = 0; i < n1; i++)
      L[i] = arr[l + i];
   for (j = 0; j < n2; j++)
      R[j] = arr[m + 1+ j];
   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++;
   }
   while (i < n1) {
      arr[k] = L[i];
      i++;
      k++;
   }
   while (j < n2) {
      arr[k] = R[j];
      j++;
      k++;
   }
}
void iterativeMergeSort(int arr[], int l, int r) {
   if (l < r){
      int mid = l+(r-l)/2;
      iterativeMergeSort(arr, l, mid);
      iterativeMergeSort(arr, mid+1, r);
      merge(arr, l, mid, r);
   }
}
int main(){
   int arr[] = {12, 11, 13, 5, 6, 7};
   int size = sizeof(arr)/sizeof(arr[0]);
   printf("\t\t ITERATIVE MERGE SORT 
");
   printf("Unsorted Array : \t");
   for (int i=0; i < size; i++)
      printf("%d ",arr[i]);
   iterativeMergeSort(arr, 0, size - 1);
   printf("
Sorted array : \t");
   for (int i=0; i < size; i++)
      printf("%d ", arr[i]);
   printf("
");
   return 0;
}

Output

ITERATIVE MERGE SORT
Unsorted Array : 12 11 13 5 6 7
Sorted array : 5 6 7 11 12 13