Another merge sort of integer list source code

This snippet submitted by Manoj on 2010-03-02. It has been viewed 12685 times.
Rating of 5.6 with 90 votes

#include <stdio.h>
#include <stdlib.h>

#define MAXARRAY 10

void mergesort(int a[], int low, int high);

int main(void) {
    int array[MAXARRAY];
    int i = 0;

    /* load some random values into the array */
    for(i = 0; i < MAXARRAY; i++)
	array[i] = rand() % 100; 

    /* array before mergesort */
    printf("Before    :");
    for(i = 0; i < MAXARRAY; i++)
	printf(" %d", array[i]);

    printf("\n");

    mergesort(array, 0, MAXARRAY - 1);

    /* array after mergesort */
    printf("Mergesort :");
    for(i = 0; i < MAXARRAY; i++)
	printf(" %d", array[i]);

    printf("\n");
    return 0;
}

void mergesort(int a[], int low, int high) {
    int i = 0;
    int length = high - low + 1;
    int pivot  = 0;
    int merge1 = 0;
    int merge2 = 0;
    int working[length];

    if(low == high)
	return;

    pivot  = (low + high) / 2;

    mergesort(a, low, pivot);
    mergesort(a, pivot + 1, high);

    for(i = 0; i < length; i++)
	working[i] = a[low + i];

    merge1 = 0;
    merge2 = pivot - low + 1;

    for(i = 0; i < length; i++) {
	if(merge2 <= high - low)
	    if(merge1 <= pivot - low)
		if(working[merge1] > working[merge2])
		    a[i + low] = working[merge2++];
		else
		    a[i + low] = working[merge1++];
	    else
		a[i + low] = working[merge2++];
	else
	    a[i + low] = working[merge1++];
    }
}

More C and C++ source code snippets