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;

}