poj1386单词连接（欧拉欧拉欧拉）

///单词连接，欧拉回路通路都可以（有向图）
///主要构图：比如possibilities就构造p->s的边
#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
const int N=26;
char s[1003];
int f[28],outd[28],ind[28];
int find(int x){
    return x==f[x]?x:f[x]=find(f[x]);
}
int main(){
    int t;
    scanf("%d",&t);
    while(t--){
        int n;
        for(int i=0;i<N;i++)
            f[i]=i;
        memset(outd,0,sizeof(outd));
        memset(ind,0,sizeof(ind));
        scanf("%d",&n);
        while(n--){
            scanf("%s",s);
            int u=s[0]-‘a‘;
            int v=s[strlen(s)-1]-‘a‘;
            ///u-->v
            int a=find(u);
            int b=find(v);
            if(a!=b)
                f[a]=b;
            outd[u]++;
            ind[v]++;
        }
        int flag=0,sum=0;
        int sum_in=0,sum_out=0;
        for(int i=0;i<N;i++){
            if(f[i]==i&&(outd[i]+ind[i])>0)
                sum++;
            if(outd[i]!=ind[i]){
                if(outd[i]+1==ind[i])
                    sum_in++;
                else if(outd[i]-1==ind[i])
                    sum_out++;
                else
                    flag=1;    
            }
        }
        if(!flag&&sum==1&&(sum_out==0&&sum_in==0||sum_in==1&&sum_out==1))
            puts("Ordering is possible.");
        else
            puts("The door cannot be opened.");
    }
    return 0;
}