问题 B: 基础排序III：归并排序

#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

void merge(int a[], int l1, int r1, int l2, int r2) {
    int i = l1, j = l2;

    int n = r2 - l1 +1;
    int temp[n];
    int index = 0;

    while (i <= r1 && j <= r2) {
        if (a[i] == a[j]) {
            temp[index++] = a[i++];
        } else if (a[i] < a[j]) {
            temp[index++] = a[i++];
        } else {
            temp[index++] = a[j++];
        }
    }

    while (i <= r1) temp[index++] = a[i++];
    while (j <= r2) temp[index++] = a[j++];

    for (int i1 = 0; i1 < n; ++i1) {
        a[l1 + i1] = temp[i1];
    }
}

void merge_sort(int a[], int left, int right) {
    if (left < right) {
        int mid = left + (right - left) / 2;
        merge_sort(a, left, mid);
        merge_sort(a, mid + 1, right);
        merge(a, left, mid, mid + 1, right);
    }

}

int main() {

    int n;
    while (scanf(" %d", &n) != EOF) {

        for (int k = 0; k < n; ++k) {
            int m;
            scanf("%d",&m);
            int a[m];
            for (int i = 0; i < m; ++i) {
                scanf("%d", &a[i]);
            }
            merge_sort(a, 0, m - 1);

            for (int j = 0; j < m; ++j) {
                printf("%d\n", a[j]);
            }
        }

    }
    return 0;
}