Given a set of sticks of various lengths, is it possible to join them end-to-end to form a square?

Input

The first line of input contains N, the number of test cases. Each test case begins with an integer 4 <= M <= 20, the number of sticks. M integers follow; each gives the length of a stick - an integer between 1 and 10,000.

Output

For each case, output a line containing “yes” if is is possible to form a square; otherwise output “no”.

Sample Input

3

4 1 1 1 1

5 10 20 30 40 50

8 1 7 2 6 4 4 3 5

Sample Output

yes

no

yes

搜边长

#include <cstdio>

#include <iostream>

#include <algorithm>

#include <cstring>

using namespace std;

int a[25];

int sum,n,s;

bool mark[25];

bool cmp(int a,int b) {

    return a>b;

}

int dfs(int step,int cur,int index) {

    if(step==3) return 1;//ye zi

    for(int i=index;i<n;i++){

        if(!mark[i]) {

            if(cur+a[i]==s) {

                mark[i]=true;

                if(dfs(step+1,0,0)) return 1;

                mark[i]=false;

            }

            else if(cur+a[i]<s){

                mark[i]=true;

                if(dfs(step,cur+a[i],i+1)) return 1;

                mark[i]=false;

            }

        }

    }

    return 0;

}

int main(){

//  freopen("INPut.txt","r",stdin);

    int t;

    scanf("%d",&t);

    while(t--) {

        memset(mark,false,sizeof(mark));

        sum=0;

        scanf("%d",&n);

        int M=0;

        for(int i=0;i<n;i++) {

            scanf("%d",&a[i]);

            sum+=a[i];

            M=max(M,a[i]);

        }

        s=sum/4;

        if(sum%4||M>s) {

            printf("no\n");

            continue;

        }

        sort(a,a+n,cmp);

        if(dfs(0,0,0)) {

            printf("yes\n");

        }

        else printf("no\n");

    }

    return 0;

}