poj 1386

要判连通性，

代码：

#include<iostream>
#include<fstream>
#include<vector>

using namespace std;

int in[30];
int out[30];
int n;
int v[30];
vector<int> edge[27];

void dfs(int s){
	v[s]=1;
	for(int i=0;i<edge[s].size();i++)
		if(v[edge[s][i]]==0)
			dfs(edge[s][i]);
}

int ok(int s){
	int i;
	
	memset(v,0,sizeof(v));
	dfs(s);
	for(i=0;i<26;i++)
		if(v[i]==0&&edge[i].size()!=0)
			return 0;
	return 1;

}

void read(){
//	ifstream cin("in.txt");
	int i,j,k;
	cin>>k;
	char c[1010];

	while(k--)
	{
		memset(in,0,sizeof(in));
		memset(out,0,sizeof(out));
		int f=0;
		cin>>n;
		for(i=0;i<26;i++)
			edge[i].clear();
		for(i=1;i<=n;i++)
		{
			cin>>c;
			out[c[0]-'a']++;
			in[c[strlen(c)-1]-'a']++;
			edge[c[0]-'a'].push_back(c[strlen(c)-1]-'a');
			edge[c[strlen(c)-1]-'a'].push_back(c[0]-'a');
		}
		if(!ok(c[0]-'a'))
		{
			cout<<"The door cannot be opened."<<endl;
			continue;
		}
			
		for(i=0;i<26;i++)
			if(in[i]!=out[i])
			{
				if(in[i]<out[i])
				{
					if(f==0&&in[i]-out[i]==-1)
					{
						f=1;
					}
					else
						break;
				}
			}
		if(i<26)
			cout<<"The door cannot be opened."<<endl;
		else
			cout<<"Ordering is possible."<<endl;
	}
}

int main(){
	read();
	return 0;
}