C program to implement MERGE sort


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Merge sort is based on the divide conquer strategy. Array is divided in to two halves.if the array length is n, then it is divided into n/2,n/4,n/8…. and each part is sorted independently, then conquered into the sorted array.

The efficiency of merge sort is O(n log n)

C Program

#include <stdio.h>
#include <stdlib.h>
#define MAX_ARY 10
void merge_sort(int x[], int end, int start);
int main(void) {
	int ary[MAX_ARY];
	int j = 0;
	printf("\n\nEnter the elements to be sorted: \n");
	for (j=0;j<MAX_ARY;j++)
	  scanf("%d",&ary[j]);
	/* array before mergesort */
	printf("Before    :");
	for (j = 0; j < MAX_ARY; j++)
	  printf(" %d", ary[j]);
	printf("\n");
	merge_sort(ary, 0, MAX_ARY - 1);
	/* array after mergesort */
	printf("After Merge Sort :");
	for (j = 0; j < MAX_ARY; j++)
	  printf(" %d", ary[j]);
	printf("\n");
	getch();
}
/* Method to implement Merge Sort*/
void merge_sort(int x[], int end, int start) {
	int j = 0;
	const int size = start - end + 1;
	int mid  = 0;
	int mrg1 = 0;
	int mrg2 = 0;
	int executing[MAX_ARY];
	if(end == start)
	  return;
	mid  = (end + start) / 2;
	merge_sort(x, end, mid);
	merge_sort(x, mid + 1, start);
	for (j = 0; j < size; j++)
	  executing[j] = x[end + j];
	mrg1 = 0;
	mrg2 = mid - end + 1;
	for (j = 0; j < size; j++) {
		if(mrg2 <= start - end)
		   if(mrg1 <= mid - end)
		    if(executing[mrg1] > executing[mrg2])
		     x[j + end] = executing[mrg2++]; else
		     x[j + end] = executing[mrg1++]; else
		    x[j + end] = executing[mrg2++]; else
		   x[j + end] = executing[mrg1++];
	}
}





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