HDU 1518 Square 搜索

Square

Time Limit : 10000/5000ms (Java/Other)   Memory Limit : 65536/32768K (Java/Other)

Total Submission(s) : 11   Accepted Submission(s) : 5

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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

#include<iostream>#include<cstring>using namespace std;int v[23],n,flag;int a[23],sum;void dfs(int p,int ans,int t){if(ans==sum/4){p++;if(p==4){flag=1;return ;}else ans=0;t=0;}if(flag)   return ;for(int i=t;i<n;i++)if(!v[i] && a[i]+ans<=sum/4){v[i]=1;dfs(p,ans+a[i],i);v[i]=0;}}int main(){int T;cin>>T;while(T--){cin>>n;int max;max=sum=0;for(int i=0;i<n;i++){cin>>a[i];sum += a[i];if(max<a[i])   max=a[i];}if(sum%4!=0 || max>sum/4)cout<<"no\n";else{memset(v,0,sizeof(v));flag=0;dfs(0,0,0);if(flag)   cout<<"yes\n";else     cout<<"no\n";}}return 0;}