Merge Sort Program in C

Merge sort is a sorting technique based on divide and conquer technique. With the worst-case time complexity being Ο(n log n), it is one of the most respected algorithms.

Implementation in C

We shall see the implementation of merge sort in C programming language here −

#include <stdio.h>

#define max 10

int a[11] = { 10, 14, 19, 26, 27, 31, 33, 35, 42, 44, 0 };
int b[10];

void merging(int low, int mid, int high) {
   int l1, l2, i;

   for(l1 = low, l2 = mid + 1, i = low; l1 <= mid && l2 <= high; i++) {
      if(a[l1] <= a[l2])
         b[i] = a[l1++];
      else
         b[i] = a[l2++];
   }
   
   while(l1 <= mid)    
      b[i++] = a[l1++];

   while(l2 <= high)   
      b[i++] = a[l2++];

   for(i = low; i <= high; i++)
      a[i] = b[i];
}

void sort(int low, int high) {
   int mid;
   
   if(low < high) {
      mid = (low + high) / 2;
      sort(low, mid);
      sort(mid+1, high);
      merging(low, mid, high);
   } else { 
      return;
   }   
}

int main() { 
   int i;

   printf("List before sorting\n");
   
   for(i = 0; i <= max; i++)
      printf("%d ", a[i]);

   sort(0, max);

   printf("\nList after sorting\n");
   
   for(i = 0; i <= max; i++)
      printf("%d ", a[i]);
}

If we compile and run the above program, it will produce the following result −

Output

List before sorting
10 14 19 26 27 31 33 35 42 44 0
List after sorting
0 10 14 19 26 27 31 33 35 42 44

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