poj_2362

Language: Default

Square

Time Limit: 3000MS		Memory Limit: 65536K
Total Submissions: 17120		Accepted: 5902

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

#include <iostream>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
#pragma warning(disable : 4996)
#define MAX 25
bool vis[MAX];
int stick[MAX];
int n,goal;
bool ans;

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

void dfs(int now, int index, int cnt)
{
	if(cnt == 3)
	{
		ans = true;
	}
	if(ans) return;
	for(int i = index; i < n; i++)
	{
		if(vis[i])
		{
			continue;
		}
		if(now + stick[i] == goal)
		{
			vis[i] = true;
			dfs(0, 0, cnt + 1);
			vis[i] = false;
		}
		else if(now + stick[i] < goal)
		{
			vis[i] = true;
			dfs(now + stick[i], i + 1, cnt);
			vis[i] = false;
			if(now == 0) 
			{
				break;
			}
		}
	}
}

int main()
{
	freopen("in.txt", "r", stdin);
	int t, Max, sum;
	cin >> t;
	while (t--)
	{
		cin >> n;
		sum = 0;
		Max = -1;
		for(int i = 0; i < n; i++)
		{
			cin >> stick[i];
			sum += stick[i];
			Max = max(Max, stick[i]);
		}
		goal = sum / 4;
		if(sum % 4)
		{
			cout << "no" << endl;
			continue;
		}
		if(Max > goal)
		{
			cout << "no" << endl;
			continue;
		}
		sort(stick, stick + n, cmp);
		memset(vis, false, sizeof(vis));
		ans = false;
		dfs(0, 0 , 0);
		if(ans)
		{
			cout << "yes" << endl;
		}
		else
		{
			cout << "no" << endl;
		}
	}
}