UVa10129,Play On Words

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>
#define maxn 100000+5
using namespace std;
string map[maxn];
int n,chu[30],ru[30],G[30][30],vst[30],f,ok,c[30],cnt,ts;
int init(){
    cin>>n;
    memset(chu,0,sizeof(chu));
    memset(ru,0,sizeof(ru));
    memset(G,0,sizeof(G));
    memset(vst,0,sizeof(vst));
    memset(c,0,sizeof(c));
    cnt=0;
    string temp;
    for (int i=0;i<n;i++){
        cin>>map[i];
        int p,q;
        p=map[i][0]-‘a‘;
        q=map[i][map[i].size()-1]-‘a‘;
        ts=p;
        if (!c[p]) {cnt++;c[p]=1;}
        if (!c[q]) {cnt++;c[q]=1;}
        G[p][q]=1;
        chu[p]++;ru[q]++;
    }    
}
int is_link(int p){
    for (int j=0;j<30;j++){
        if (G[p][j]&&!vst[j]){
            vst[j]=1;
            f++;
            is_link(j);
        }
    }
}
int find_start(){
    int i;
    for ( i=0;i<30;i++)
        if (chu[i]-ru[i]==1) return i;
    if (i==30) return ts;
    //cout<<"find"<<ok<<endl;
}
int work(){
    int t=0,f=0;
    for (int i=0;i<30;i++)        
            if (chu[i]!=ru[i]){
                if (abs(chu[i]-ru[i])==1)t++;
                else f=1;
            }
    if ((t==0&&f==0)||(t==2)) return 1;
    return 0;
}
int main()
{
    int T;
    cin>>T;
    while (T--){
        init();
        ok=1;
        int p;
        p=find_start();
        vst[p]=1;
        f=1;
        if (ok)is_link(p);
        if (f!=cnt) ok=0;
        if (ok) ok=work();
        if (ok) cout<<"Ordering is possible."<<endl;
        else cout<<"The door cannot be opened."<<endl;
    }
}