【暴力搜索】[HDU 1518]Square

先说好，我的程序速度很慢1018ms。。其实就是算出总长度除以4然后搞一下和http://blog.csdn.net/jeremygjy/article/details/47043161一样的剪枝就好了。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
const int MAXN = 20;
int n, s[MAXN+10];
bool vis[MAXN+10];
int sum ;
bool dfs(int u, int up, int _len){
    //printf("%d\n", _len);
    if(u == 3){return true;}
    for(int i=up;i<n;i++) if(!vis[i] && s[i] + _len <= sum){
        vis[i] = true;
        if(s[i] + _len == sum && dfs(u+1, 0, 0)) return true;
        else if(s[i] + _len < sum  && dfs(u, i+1, s[i]+_len)) return true;
        vis[i] = false;
    }
    return false;
}
int main(){
    int T;
    scanf("%d", &T);
    while(T--){
        memset(vis, 0, sizeof vis);
        scanf("%d", &n);
        sum = 0;
        for(int i=0;i<n;i++){
            scanf("%d",  &s[i]);
            sum += s[i];
        }
        sort(s, s+n);
        //printf("%d\n", sum);
        if(sum % 4 != 0){
            printf("no\n");
            continue;
        }
        sum >>= 2;
        //printf("%d\n", sum);
        if(dfs(0, 0, 0)){
            printf("yes\n");
        }else printf("no\n");
    }

    return 0;
}