hdu 1518 Square

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

34 1 1 1 15 10 20 30 40 508 1 7 2 6 4 4 3 5

 

Sample Output

yesnoyes

给出M根棍子，要将所有棍子用上，拼成一个正方形。

#include<iostream>#include<stdio.h>#include <string.h>#include <algorithm>using  namespace std;int s[25],m,a,sum;bool vis[25];bool dfs(int cnt,int now,int k){    if(cnt==5)    {        return true;    }    for (int i=k; i<m; i++)    {        if(!vis[i])        {            if(now+s[i]<a)            {                vis[i]=true;                if(dfs(cnt,now+s[i],i+1))                {                    return true;                }                vis[i]=false;            }            if(now+s[i]==a)            {                vis[i]=true;                if(dfs(cnt+1,0,0))                {                    return true;                }                vis[i]=false;            }        }    }    return false;}int main(){    int t,i;    scanf("%d",&t);    while (t--)    {        scanf("%d",&m);        sum=0;        memset(vis, false, sizeof(vis));        for (i=0; i<m; i++)        {            scanf("%d",&s[i]);            sum+=s[i];        }        if(sum%4!=0)        {            printf("no\n");            continue;        }        a=sum/4;        sort(s, s+m, greater<int>());        if(s[0]>a)        {            printf("no\n");            continue;        }        if(dfs(1,0,0))        {            printf("yes\n");        }        else        {            printf("no\n");        }    }    return 0;}