topcoder srm 682 div1 -3

#include <stdio.h>
#include <string.h>
#include <string>
#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <algorithm>
#include <stack>
#include <assert.h>
using namespace std;

const int N=2005;


vector<int > g[N];
int h[N];

int dfs(int u,int pre,int cnt)
{
    if(cnt==5) return 1;
    h[u]=1;
    for(int i=0;i<(int)g[u].size();++i)
    {
        int v=g[u][i];
        if(v!=pre&&!h[v]&&dfs(v,u,cnt+1))
            return 1;
    }
    h[u]=0;
    return 0;
}


class SmilesTheFriendshipUnicorn
{
public:
	string hasFriendshipChain(int n,vector<int> A,vector<int> B)
	{
	    const int m=(int)A.size();

	    for(int i=0;i<m;++i)
        {
            int u=A[i];
            int v=B[i];

            g[u].push_back(v);
            g[v].push_back(u);
        }
        for(int i=0;i<n;++i)
        {
            memset(h,0,sizeof(h));
            if(dfs(i,-1,1)) return "Yay!";
        }

        return ":(";
	}
};