POJ 2362 / SCAU 2542 Square

2542 Square

时间限制:3000MS  内存限制:65536K

题型: 外判编程题   语言: 无限制

Description

Given a set of sticks of various lengths, is it possible to join them end-to-end to form a square?

输入格式

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.

输出格式

For each case, output a line containing "yes" if is is possible to form a square; otherwise output "no".

输入样例

3
4 1 1 1 1
5 10 20 30 40 50
8 1 7 2 6 4 4 3 5

输出样例

yes
no
yes

来源

Waterloo local 2002.09.21 

作者

admin

#include<iostream>
 #include<cstdio>
 #include<string>
 #include<cstring>
 #include<algorithm>
 #define MAXN 22

 using namespace std;

 int sticks[MAXN];
 bool visit[MAXN];
 int n, length, sumlen;

 bool cmp(const int& a, const int& b)
 {
     return a>b;
 }

 bool Traverse(int num, int len, int cur)
 {
     if(num == 4) return true;
     for(int i=cur; i<n; ++i)
     {
         if(!visit[i] && !(i && !visit[i-1] && sticks[i] == sticks[i-1]))
         {
             if(len+sticks[i] == length)
             {
                 visit[i] = true;
                 if(Traverse(num+1, 0, 0)) return true;
                 visit[i] = false;
                 return false;
             }
             else if(len+sticks[i] < length)
             {
                 visit[i] = true;
                 if(Traverse(num, len+sticks[i], i+1)) return true;
                 visit[i] = false;
                 if(len == 0) return false;
             }
         }
     }
     return false;
 }


 int main()
 {
     #ifndef ONLINE_JUDGE
  //   freopen("F:\\test\\input.txt", "r", stdin);
     #endif // ONLINE_JUDGE
     int t;
     cin>>t;
     while(t--)
     {
         sumlen = 0;
         cin>>n;
         for(int i=0; i<n; ++i)
         {
             cin>>sticks[i];
             sumlen += sticks[i];
         }
         sort(sticks, sticks+n, cmp);
         length = sumlen/4;
         if(sumlen%4 || length < sticks[0])
         {
             cout<<"no"<<endl;
             continue;
         }
         memset(visit, false, sizeof(visit));
         if(Traverse(0, 0, 0)) cout<<"yes"<<endl;
         else cout<<"no"<<endl;
     }
     return 0;
 }