hdu1116

http://acm.hdu.edu.cn/showproblem.php?pid=1116

#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include<iostream>
using namespace std;
const int N=30;
int father[N],vis[N];
int find(int x)//查找根
{
    if(father[x]!=x)
    father[x]=find(father[x]);
    return father[x];
}
void make(int a,int b)//合并操作
{
    int f1=find(a);
    int f2=find(b);
    if(f1!=f2)
    father[f1]=f2;
}

int main()
{
    //freopen("in.txt","r",stdin);
    int t;
    cin>>t;
    while(t--)
    {
        int out[N],in[N],p[N];
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        memset(vis,0,sizeof(vis));
        int n;
        for(int i=0;i<26;i++)
        father[i]=i;//数组赋初值
        cin >> n;
        while(n--)
        {
            char str[1005];
            cin>>str;
            int a=str[0]-'a';
            int b=str[strlen(str)-1]-'a';
            out[a]++;
            in[b]++;
            make(a,b);//合并操作
            vis[a]=vis[b]=1;
        }
        for(int i=0;i<26;i++)
        father[i]=find(i);//寻找每个点的根节点
        int cnt=0;
        for(int i=0;i<26;i++)
        {
            if(vis[i] && father[i]==i)//确定有几颗树
            cnt++;
        }
        if(cnt>1)
        {
            printf("The door cannot be opened.
");
            continue;
        }
        int j=0;
        for(int i=0;i<26;i++)
        {
            if(vis[i] && out[i]!=in[i])//找起点和终点
            p[j++]=i;
        }
        if(j==0)//环
        {
            printf("Ordering is possible.
");
            continue;
        }
        if(j==2 && ((out[p[0]]-in[p[0]]==1 && in[p[1]]-out[p[1]]==1 ) ||
                    (in[p[0]]-out[p[0]]==1 && out[p[1]]-in[p[1]]==1 ) ) )
        {//起点和终点的判断
            printf("Ordering is possible.
");
            continue;
        }
        printf("The door cannot be opened.
");
    }
    return 0;
}