HDU1518 Square

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
int L,n;
int l[21];
bool vis[21];
int dfs(int nused,int left,int pos){
    if(nused==0&&left==0) return 1;
    if(left==0)left=L;
    for(int i=pos;i<n;i++){
        if(!vis[i]&&left>=l[i]){
            if(i>0&&!vis[i-1]&&l[i]==l[i-1]) continue;
            vis[i]=1;
            if(left==l[i]){
                if(dfs(nused-1,left-l[i],0)) return 1;
                else{
                    vis[i]=0;
                    return 0;
                }
            }
            else{
                if(dfs(nused-1,left-l[i],i+1)) return 1;
                else vis[i]=0;
            }
        }
    }
    return 0;
}
int main()
{
    int i,N,sum;
    scanf("%d",&N);
    while(N--){
        memset(vis,0,sizeof(vis));
        scanf("%d",&n);
        for(sum=i=0;i<n;i++){
            scanf("%d",&l[i]);
            sum+=l[i];
        }
        if(sum%4!=0){
            printf("no\n");
            continue;
        }
        L=sum/4;
        sort(l,l+n,greater<int >());
        if(l[0]>L){
            printf("no\n");
            continue;
        }
        if(dfs(n,L,0)) printf("yes\n");
        else printf("no\n");
    }
    return 0;
}