归并排序

#include <cstdio>

int main() {
    void MergeSort(int *a, int p, int q, int r);
    const int MAXLEN = 10;
    int a[MAXLEN] = {3, 8, 9, 1, 0, 2, 5, 7, 4, 6};

    printf("befor sort:");
    for(int i=0; i<MAXLEN; ++i) {
        printf("%d ", a[i]);
    }
    putchar('\n');

    MergeSort(a, 0, (0+MAXLEN)>>1, MAXLEN);

    printf("after sort:");
    for(int i=0; i<MAXLEN; ++i) {
        printf("%d ", a[i]);
    }
    putchar('\n');

    return 0;
}

void MergeSort(int *a, int p, int q, int r) {
    if (p==q || q==r) return;

    MergeSort(a, p, (p+q)>>1, q);
    MergeSort(a, q, (q+r)>>1, r);

    for (int i=q; i<r; ++i) {
        int k = i;
        int tmp = a[i];
        for (int j=i-1; j>=p && a[j]>tmp; --j) {
            a[j+1] = a[j];
            k = j;
        }
        if (k == i) {
            break;
        }
        else {
            a[k] = tmp;
        }
    }
}