Square

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 13374    Accepted Submission(s): 4244

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

 

 

Source

 

题意:问n根木棍能否组成一个正方形?

题解:排序+暴力+剪枝。。那些15ms的大神是怎么做到的。。

#include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           using namespace std;int v[25];int n;int sum = 0;bool vis[25];bool flag;//cnt代表当前到第几根了,len代表当前木棍长度void dfs(int cnt,int len,int now){    if(cnt==4){        flag = true;        return;    }    for(int i=now;i
           
            len+v[i]){ vis[i] = true; dfs(cnt,len+v[i],i+1); vis[i] = false; } }}int cmp(int a,int b){ return a>b;}int main(){ int tcase; scanf("%d",&tcase); while(tcase--){ scanf("%d",&n); sum = 0; for(int i=0;i
            
             sum) { printf("no\n"); continue; } memset(vis,false,sizeof(vis)); flag = false; dfs(0,0,0); if(flag) printf("yes\n"); else printf("no\n"); }}