归并排序

归并排序

1、确定分界点：mid = (l + r) / 2

2、递归排序left, right

3、归并 合二为一

模板

注意l 和 1 的区分

#include<bits/stdc++.h> //万能头文件
using namespace std;

const int N = 1000010;
int n;
int q[N], tmp[N];

//模板
void merge_sort(int q[], int l, int r) {
    if (l >= r) {
        return;
    }
    int mid = l + r >> 1;

    merge_sort(q, l, mid);
    merge_sort(q, mid + 1, r);

    int k = 0, i = l, j = mid + 1;
    while (i <= mid && j <= r) {
        if (q[i] <= q[j]) {
            tmp[k++] = q[i++];
        } else {
            tmp[k++] = q[j++];
        }
    }
    while (i <= mid) {
        tmp[k++] = q[i++];
    }
    while (j <= r) {
        tmp[k++] = q[j++];
    }
    for (i = l, j = 0; j <= r; i++, j++) {
        q[i] = tmp[j];
    }
}


int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &q[i]);

    merge_sort(q, 0, n - 1);

    for (int i = 0; i < n; i++) printf("%d ", q[i]);
    return 0;

}