HDOJ 5424 Rikka with Graph II 暴力dfs

哈密顿路径本来是NPC的问题,不过这题可以特判后直接暴力dfs

Rikka with Graph II

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 1066    Accepted Submission(s): 271

Problem Description

As we know, Rikka is poor at math. Yuta is worrying about this situation, so he gives Rikka some math tasks to practice. There is one of them:

Yuta has a non-direct graph with  n  vertices and  n  edges. Now he wants you to tell him if there exist a Hamiltonian path.

It is too difficult for Rikka. Can you help her?

 

Input

There are no more than 100 testcases. 

For each testcase, the first line contains a number  n(1≤n≤1000) .

Then  n  lines follow. Each line contains two numbers  u,v(1≤u,v≤n)  , which means there is an edge between  u  and  v .

 

Output

For each testcase, if there exist a Hamiltonian path print "YES" , otherwise print "NO".

 

Sample Input

   
   
   
   

    
    
    
    4
1 1
1 2
2 3
2 4
3
1 2
2 3
3 1
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    NO
YES

Hint
For the second testcase, One of the path is 1->2->3
If you doesn't know what is Hamiltonian path, click here (https://en.wikipedia.org/wiki/Hamiltonian_path).
   
   
   
   

 

Source

BestCoder Round #53 (div.2)

 

/* ***********************************************
Author        :CKboss
Created Time  :2015年09月03日 星期四 08时33分46秒
File Name     :HDOJ5424.cpp
************************************************ */

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;

const int maxn=1100;

int fa[maxn];

int Find(int x)
{
	return (x==fa[x])?x:fa[x]=Find(fa[x]);
}

void Union(int u,int v)
{
	u=Find(u); v=Find(v);
	if(u==v) return ;
	fa[u]=v;
}

int n,du[maxn];
bool vis[maxn];
vector<int> G[maxn];
bool flag;

void dfs(int u,int c)
{
	if(flag) return ;
	if(c==n)
	{
		flag=true; return ;
	}
	for(int i=0,sz=G[u].size();i<sz;i++)
	{
		int v=G[u][i];
		if(vis[v]==true) continue;
		vis[v]=true;
		dfs(v,c+1);
		vis[v]=false;
	}
}

int main()
{
	//freopen("in.txt","r",stdin);
	//freopen("out.txt","w",stdout);

	while(scanf("%d",&n)!=EOF)
	{
		memset(du,0,sizeof(du));
		memset(vis,0,sizeof(vis));
		for(int i=1;i<=n;i++) 
		{
			G[i].clear(); fa[i]=i;
		}

		for(int i=0;i<n;i++)
		{
			int u,v;
			scanf("%d%d",&u,&v);
			G[u].push_back(v); G[v].push_back(u);
			du[u]++; du[v]++;
			Union(u,v);
		}
		int st=1,g=Find(st);
		bool ok=true;
		for(int i=2;i<=n;i++)
		{
			if(du[i]<du[st]) st=i;
			if(Find(i)!=g) ok=false;
		}
		if(ok==false) 
		{
			puts("NO"); continue;
		}
		flag=false;
		vis[st]=true;
		dfs(st,1);
		if(flag) puts("YES");
		else puts("NO");
	}
    
    return 0;
}