学步园

/**//**************************************
Problem: HEU 1011 Square
Time: 0.0400 s
Memory: 232 k 
Accepted Time: 2009-03-22 14:08:04
Tips: 深度优先搜索 http://acm.hrbeu.edu.cn/forums/index.php?showtopic=2305&hl=1011
**************************************/
#include <stdio.h>
#include <string.h>
int sign,ave,length;
int a[100],table[100];
void dfs(int start,int sum,int flag)
{
    if(flag==4){sign=1;return;}
    else if(sign==0)
    {
        if(sum==ave)dfs(0,0,flag+1);
        else for(int i=start;i<length;i++)
        {
            if(table[i]==0&&sum+a[i]<=ave)
            {
                table[i]=1;
                dfs(i+1,sum+a[i],flag);
                table[i]=0;
            }
        }
    }
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int i,j,k,sum=0;
        scanf("%d",&length);
        for(i=0;i<length;i++)
        {
            scanf("%d",&a[i]);
            sum+=a[i];
        }
        if(sum%4!=0){printf("no\n");continue;}
        for(i=0;i<length-1;i++)
        {
            k=i;
            for(j=i+1;j<length;j++)
            if(a[k]<a[j])k=j;
            if(k!=i)
            {int tt=a[k]; a[k]=a[i]; a[i]=tt;}
        }
        ave=sum/4;
        if(a[0]>ave){printf("no\n");continue;}
        memset(table,0,sizeof(table));
        sign=0;
        dfs(0,0,1);
        if(sign)printf("yes\n");
        else printf("no\n");
    }
    return 0;
}