自然合并排序算法

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

void merge(int *a, int p, int q, int r)
{
        int s1, e1;
        int s2, e2;
        int *temp = malloc((r-p+1) * sizeof(int));
        memset(temp, 0, sizeof(int));
        s1 = p; e1 = q;
        s2 = q+1; e2 = r;
        int index = s1;
        int i = 0;
        while(s1 <= e1 && s2 <= e2) {
                if (a[s1] < a[s2]) {
                        temp[i++] = a[s1];
                        s1++;
                }
                else {
                        temp[i++] = a[s2];
                        s2++;
                }
        }
        while (s1 < e1+1) {
                temp[i++] = a[s1];
                s1++;
        }
        while (s2 < e2+1) {
                temp[i++] = a[s2];
                s2++;
        }
        for (i = 0; i < r-p+1; i++) {
                a[index + i] = temp[i];
        }
        free(temp);
}

void naturalMergeSort(int *a, int n)
{
        int *index = malloc(n*sizeof(int));
        memset(index, 0, sizeof(int));
        int k = 1;
        int i;
        for (i = 0; i < n - 1; i++) {
                if (a[i] > a[i+1]) {
                        index[k++] = i;
                }
        }
        index[k] = n - 1;
        int s = 1;
        for (i = k; i > 1; i = (i % 2 == 0 ? (i / 2) : (i / 2 + 1))) {
                int count = i / 2;
                int p = 0;
                int q = s;
                int r = 2*s;
                if (r > k ) {
                        r = k - 1;
                }
                merge(a, index[p], index[q], index[r]);
                int j;
                for (j = 1; j < count; j++) {
                        p = r;
                        q = p + s;
                        r = q + s;
                        if (r > k) {
                                r = k -1;
                        }
                        merge(a, index[p] + 1, index[q], index[r]);
                }
                s += s;
        }
}

int main()
{
        int a[8] = {4, 8, 3, 7, 1, 5, 6, 2};
        naturalMergeSort(a, 8);
        int i;
        for (i = 0; i < 8; i++) {
                printf("%d ", a[i]);
        }
        printf("\n");
        return 0;
}