> #include<stdio.h>
> #include<memory.h>
> #include<stdlib.h>
> #include<string.h>
> 
> 
> #ifdef debug
> #define input file
> FILE*file=fopen("tmp.txt","r");
> #else
> #define input stdin
> #endif
> 
> #define SIZE 100000
> #define WORD 1000
> 
> int in[26];             //入度出度判欧拉路径
> int out[26];
> int visited[26];
> int uset[26];           //并查集判联通
> int T,N;
> 
> int root(int i){
>     if(uset[i]==i)return i;
>     uset[i]=root(uset[i]);
>     return uset[i];
> }
> 
> void combine(int i,int j){
>     uset[uset[j]]=uset[i];
> }        
>             
>     
> 
> int main(){
>     fscanf(input,"%d",&T);
>     while(T--){
>         fscanf(input,"%d",&N);
>         int i,j;
>         char s[WORD+1];
>         memset(in,0,sizeof(in));
>         memset(out,0,sizeof(out));
>         memset(visited,0,sizeof(visited));
>         for(i=0;i<26;i++){
>             uset[i]=i;
>         }    
>         for(i=0;i<N;i++){
>             fscanf(input,"%s",s);
>             int first,last;
>             first=s[0]-'a';
>             last=s[strlen(s)-1]-'a';
>             
>             in[first]++;
>             out[last]++;
>             visited[first]=1;
>             visited[last]=1;
>             if(root(first)!=root(last))combine(first,last);
>         }
>         int num_in=0,num_out=0;
>         for(i=0;i<26;i++){                 //判欧拉路径
>             if(!visited[i])continue;
>             if(in[i]!=out[i]){
>                 if(in[i]==(out[i]-1))num_in++;
>                 else if(in[i]==(out[i]+1))num_out++;
>                 else break;
>             }
>         }
>         if(i<26||(num_in!=1)||(num_out!=1)){
>             printf("The door cannot be opened.\n");
>             continue;
>         }
>         for(i=0;i<26;i++){          //判联通
>             if(visited[i])break;
>         }
>         int _root=root(i);
>         for(i++;i<26;i++){
>             if(visited[i]&&root(i)!=_root)break;
>         }
>         if(i<26){
>             printf("The door cannot be opened.\n");
>             continue;
>         }
>         printf("Ordering is possible.\n");
>     }
>     system("pause");
>     return 0;
> }                          
>