归并排序

先递归为多个小部分再进行排序

#include <iostream>

using namespace std;
const int N = 1e5 + 10;
int a[N], tem[N];

void merge_sort(int a[], int l, int r)
{
	if (l >= r) return;
	
	int mid = l + r >> 1;
	merge_sort(a, l, mid), merge_sort(a, mid + 1, r); //递归分为两部分
	
	int i = l, j = mid + 1, k = 0;
	while (i <= mid && j <= r) //取两部分中最小的值放入另一个数列
		if (a[i] <= a[j]) tem[k ++] = a[i ++];
	else tem[k ++] = a[j ++];
	while (i <= mid) tem[k ++] = a[i ++];  
	while (j <= r) tem[k ++] = a[j ++];
	
	for (i = l, j = 0;i <= r;i ++, j ++) a[i] = tem[j]; 
}


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