<span>POJ1386 Play on Words</span>

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <cstdio>
using namespace std;
int n,father[30],range[30],save[100010],in[30],out[30];
bool use[30];
char s[1010];
void add(int x)
{
    use[x]=true;
    father[x]=x;
    range[x]=0;
}
int Find(int x)
{
    int k=0;
    while(x!=father[x])
    {
        save[k++]=x;
        x=father[x];
    }
    for(int j=0; j<k; j++)
        father[save[j]]=x;
    return x;
}
void uni(int x,int y)
{
    int a=Find(x),b=Find(y);
    if(a!=b)
    {
        if(range[a]<range[b]) father[a]=b;
        else
        {
            father[b]=a;
            if(range[a]==range[b]) range[a]++;
        }
    }
}
int main()
{
    freopen("in.txt","r",stdin);
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        memset(use,false,sizeof(use));
        memset(father,0,sizeof(father));
        memset(range,0,sizeof(range));
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        for(int i=1; i<=n; i++)
        {
            scanf("%s",s);
            int l=strlen(s),x=s[0]-'a',y=s[l-1]-'a';
            if(use[x]==false) add(x);
            if(use[y]==false) add(y);
            in[x]++;
            out[y]++;
            uni(x,y);
        }
        int flag=0;
        for(int i=0; i<26; i++)
        {
            if(use[i]==true&&Find(i)==i)
            {
                flag++;
            }
        }
        if(flag>1) printf("The door cannot be opened.\n");
        else
        {
            int a=0,b=0,i;
            for(i=0;i<26;i++)
            {
                if(use[i]&&in[i]!=out[i])
                {
                    if(in[i]-out[i]==1) a++;
                    else if(out[i]-in[i]==1) b++;
                    else break;
                }
            }
            if(i<26) printf("The door cannot be opened.\n");
            else if(a+b==0||a==1&&b==1) printf("Ordering is possible.\n");
            else printf("The door cannot be opened.\n");
        }
    }
    return 0;
}