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

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.

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

3

4 1 1 1 1

5 10 20 30 40 50

8 1 7 2 6 4 4 3 5

yes

no

yes

University of Waterloo Local Contest 2002.09.21

#include <iostream>

#include<cstdio>

#include<algorithm>

#include<cstring>

using namespace std;

int t,i,j,n,m,flag,sum,ans;

int vis[],a[];

int cmp(int a,int b)

{

    return a>b;

}

void dfs(int k,int l,int edge)

{

     if(edge==)

     {

         flag=;

         return;

     }

  //  if(flag) return;

    for(int i=k;i<=n;i++)

     if (!vis[i])

        if (l+a[i]<=sum)

    {

        vis[i]=;

        if (l+a[i]==sum)  dfs(,,edge+);

           else dfs(i+,l+a[i],edge);

        if(flag) return;

        vis[i]=;

    }

    return;

}

int main()

{

    scanf("%d",&t);

    for(;t>;t--)

    {

        scanf("%d",&n);

        sum=;

        for(i=;i<=n;i++)

        {

            scanf("%d",&a[i]);

            sum+=a[i];

        }

        if (sum%!=)

        {

            printf("no\n");

            continue;

        }

        sort(a+,a++n,cmp);

        sum=sum/;

        if (a[]>sum)

        {

            printf("no\n");

            continue;

        }

        memset(vis,,sizeof(vis));

        flag=;

        dfs(,,);

        if(flag) printf("yes\n");

          else printf("no\n");

    }

    return ;

}