归并排序

  • 算法板子
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#include <iostream>
#include <cstdio>

using namespace std;
const int N = 1e8 + 9;

int a[N], tmp[N];

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 = 1, 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 = 1; i <= r;i ++, j ++) q[i] = tmp[j]; // 注意 j 从数组的起点开始
}

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

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