题目

归并排序

思路

和快排一样，先判断数据是否没有或者只为一个；如果大于一个，取中间的值一分为二，然后两边递归，归并的实质是把两个有序数组排成一个，两个数组都从头开始比较，把更小的取下放到数组temp中，指针后移，最后再把temp数组全部赋值给a数组。

代码

#include<iostream>
using namespace std;
const int N = 100010;
int n;
int a[N], temp[N];
void merge_sort(int a[], int l, int r)
{if (l >= r){return;}int mid = (l + r) / 2;merge_sort(a, l, mid), merge_sort(a, mid + 1, r);int k = 0, i = l, j = mid + 1;while (i <= mid && j <= r){if (a[i] <= a[j]){temp[k++] = a[i++];}else{temp[k++] = a[j++];}}while (i <= mid){temp[k++] = a[i++];}while (j <= r){temp[k++] = a[j++];}for (int i = l, j = 0;i <= r;i++, j++){a[i] = temp[j];}
}
int main()
{cin >> n;for (int i = 0;i < n;i++){cin >> a[i];}merge_sort(a, 0, n - 1);for (int i = 0;i < n;i++){cout << a[i] << " ";}return 0;
}