杭电1518

Square

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 12082    Accepted Submission(s): 3855

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.

#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;

bool cmp(int a,int b)
{
	return a<b;
}

int a[100];
int vis[100];
int k,n,s;

void dfs(int sum,int x,int d)
{
	if(k||x==3)
	{
		k=1;return ;
	}
	int i;
	for(i=d;i<n;i++)
	{
		if(k)
		return ;
		if(!vis[i])
		{
			if(sum+a[i]==s)
			{
				vis[i]=1;
				dfs(0,x+1,0);
				vis[i]=0;
			}
			else if(sum+a[i]<s)
			{
				vis[i]=1;
				dfs(sum+a[i],x,i+1);
				vis[i]=0;
			}
		}
	}
}

int main()
{
	int t,i;
	cin>>t;
	while(t--)
	{
		memset(vis,0,sizeof(vis));
		cin>>n;
		s=0;
		for(i=0;i<n;i++)
		{
			cin>>a[i];
			s+=a[i];
		}
		sort(a,a+n,cmp);
		if(s%4==0)
		{
			s/=4;
			k=0;
			dfs(0,0,0);
			if(k)
			cout<<"yes"<<endl;
			else
			cout<<"no"<<endl;
		}
		else
		cout<<"no"<<endl;
	}
	return 0;
}


本代码为借助，很经典

 

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

University of Waterloo Local Contest 2002.09.21