HDU 1116

#include<cstdio>
#include<cstring>
int fa[26],in[26],out[26];
int findset(int x)
{
    if(fa[x]==x) return fa[x];
    return fa[x]=findset(fa[x]);
}
bool vis[26];
char s[1010];
int main()
{
    int T,n;
    scanf("%d",&T);
    while(T--){
        scanf("%d",&n);
        getchar();
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        memset(vis,0,sizeof(vis));
        for(int i=0;i<26;i++) fa[i]=i;
        while(n--){
            gets(s);
            int x=s[0]-‘a‘;
            out[x]++;
            int y=s[strlen(s)-1]-‘a‘;
            in[y]++;
            fa[y]=findset(x);
            vis[x]=vis[y]=1;
        }
        int scc=0;
        for(int i=0;i<26;i++){
            if(vis[i]&&fa[i]==i)
                scc++;
        }
        if(scc>1){//如果不连通 
            printf("The door cannot be opened.\n");
            continue;
        }
        bool flag=false;
        int x=0,y=0,z=0;
        for(int i=0;i<26;i++){
            if(vis[i]&&in[i]!=out[i]){
                if(in[i]==out[i]+1)
                    x++;
                else if(in[i]+1==out[i])
                    y++;
                else z++;
            }
        }
        if(z){
            printf("The door cannot be opened.\n");
            continue;
        }
        if((x==1&&y==1)||(x==0&&y==0)){
            printf("Ordering is possible.\n");
            continue;
        }
        else
            printf("The door cannot be opened.\n");
    }
    return 0;
}