题解 | #神奇的口袋#

#include <cstdio>
#include <iostream>
#include <algorithm>

using namespace std;

const int MAXN = 20;

int things[MAXN];

void DFS(int step, int n, int pos, int sum, int *ans){//n是物品总数； 预先排序 
	if(step > n){
		return;
	}
	for(int i=pos; i<n; i++){
		sum += things[i];
		if(sum > 40){
			return;
		}else if(sum == 40){
			*ans += 1;
		}else if(sum < 40){
			DFS(step+1, n, i+1, sum, ans);//一路return回去的设计是“搜到即可”，但本题是要计数 
		}
		sum -= things[i];
	}
	return;
}

int main(){
	int n;
	while(scanf("%d",&n) != EOF){
		for(int i=0; i<n; i++){
			scanf("%d",&things[i]);
		}
		int ans = 0;
		sort(things, things+n);
		DFS(1,n,0,0,&ans);
		printf("%d\n",ans);
		
	} 
	return 0;
}