poj1386

欧拉通路

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

int n;
char st[1005];
bool exist[30];
int in[30], out[30];
int father[30];

int getanc(int a)
{
    if (father[a] == a)
        return a;
    return father[a] = getanc(father[a]);
}

void merge(int a, int b)
{
    father[getanc(a)] = getanc(b);
}

void input()
{
    scanf("%d", &n);
    memset(in, 0, sizeof(in));
    memset(out, 0, sizeof(out));
    memset(exist, 0, sizeof(exist));
    for (int i = 0; i < 26; i++)
        father[i] = i;
    for (int i = 0 ; i < n; i++)
    {
        scanf("%s", st);
        in[st[0] - 'a']++;
        out[st[strlen(st) - 1] - 'a']++;
        merge(st[0] - 'a', st[strlen(st) - 1] - 'a');
        exist[st[0] - 'a'] = exist[st[strlen(st) - 1] - 'a'] = true;
    }
}

bool ok()
{
    int start =0;
    int end = 0;
    int cnt = 0;
    for (int i = 0; i < 26; i++)
        if (father[i] == i && exist[i])
            cnt++;
    if (cnt > 1)
        return false;
    for (int i = 0; i < 26; i++)
        if (in[i] - out[i] == 1)
            start++;
        else if (out[i] - in[i] == 1)
            end++;
        else if (out[i] == in[i])
            continue;
        else
            return false;
    return start <= 1 && end <= 1;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    int t;
    scanf("%d", &t);
    while (t--)
    {
        input();
        if (ok())
            printf("Ordering is possible.\n");
        else
            printf("The door cannot be opened.\n");
    }
    return 0;
}