hdu 1518 Square （广搜）

Problem Description

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

 

 

#include<iostream>
using namespace std;

int num[30] , len;
int vis[30];
int n , m;
int count;
int dfs(int start , int s , int count)
{
    if(s == len)
    {
        if(count == 3)   //跳出递归
        {return 1;}
        else
        {return dfs(0,0,count+1);}
    }
    else
    {
        int i;
        for(i = start ; i < m; i++)
        {
            if(vis[i]) continue;
            if(s + num[i] > len) continue;
            vis[i] = 1;
            if(dfs(i+1 , s + num[i] , count))
                return 1;
            vis[i] = 0;
        }
    }
    return 0;
}
int main()
{
    int i , sum , flag;
    cin>>n;
    while(n--)
    {
        sum = 0;
        cin>>m;
        count = 0;
        flag = 1;
        memset(vis , 0 , sizeof(vis));
        for(i = 0; i < m; i++)
        { 
            cin>>num[i];
            sum += num[i];
        }
        if(sum % 4) {cout<<"no"<<endl; flag = 0;}
        len = sum / 4;
        if(flag)
        {
            if(dfs(0 , 0 , 0))
                cout<<"yes"<<endl;
            else cout<<"no"<<endl;
        }
    }
    return 0;
}