ACM篇：Uva 10129 -- Play on Words

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <sstream>
#include <cstdlib>
#include <vector>
#include <stack>
#include <assert.h>
using namespace std;
const int N = 26;
const int LENGTH = 1024;

bool G[N+2][N+2];
bool pot[N+2];
int in[N+2];
int out[N+2];

void build_G()
{
    int m;
    char s[LENGTH];
    memset(pot, 0, sizeof(pot));
    memset(G, 0, sizeof(G));
    memset(in, 0, sizeof(in));
    memset(out, 0, sizeof(out));
    scanf("%d", &m);
    while (m-- > 0)
    {
        scanf("%s", s);
        int u = s[0] - 'a' + 1;
        int v = s[strlen(s)-1] - 'a' + 1;
        G[u][v] = true;
        pot[u] = pot[v] = true;
        out[u]++;
        in[v]++;
    }
}

bool vis[N+2];
void _dfs(int u)
{
    vis[u] = true;
    for (int v = 1; v <= N; v++)
        if ((G[u][v] || G[v][u]) && !vis[v])
            _dfs(v);
}
bool is_joint()
{
    memset(vis, 0, sizeof(vis));

    for (int u = 1; u <= N; u++)
        if (pot[u] && !vis[u])
        {
            _dfs(u);
            break;
        }
    for (int u = 1; u <= N; u++)
        if (pot[u] && !vis[u])
            return false;
    return true;
}

bool io_check()
{
    bool begin = false;
    bool end = false;
    for (int u = 1; u <= N; u++)
    {
        if (pot[u] && in[u] != out[u])
        {
            if (out[u] == in[u] + 1)
            {
                if (begin)
                    return false;
                begin = true;
            }
            else if (in[u] == out[u] + 1)
            {
                if (end)
                    return false;
                end = true;
            }
            else
                return false;
        }
    }
    return true;
}
int main()
{
    int T;
    scanf("%d", &T);
    while (T-- > 0)
    {
        build_G();

        if (is_joint() && io_check())
            printf("Ordering is possible.\n");
        else 
            printf("The door cannot be opened.\n");
    }
    return 0;
}