解题思路：就是在给定的无向图上搜寻给定起点至给定终点间最短路径的问题。

恶心的输入案例，硬将输入拆成两半，把我这个资深强迫症患者折磨得要死。用 getchar/ungetc、cin.get()/cin.unget() 贡献若干次 TLE 后，终于成功……说服自己放弃。

代码：

#include 
    
     #include 
     
      const int MAX = 21;int countries[MAX][MAX];int main() {    int n, v, c = 1;    while (scanf("%d", &n) != EOF) {		// 构建邻接矩阵        memset(countries, MAX, sizeof(countries));        while (n--) {            scanf("%d", &v);            countries[1][v] = 1;            countries[v][1] = 1;        }        for (int i = 2; i < 20; ++i) {            scanf("%d", &n);            while (n--) {                scanf("%d", &v);                countries[i][v] = 1;                countries[v][i] = 1;            }        }		// Floyd-Warshall 算法		// 很直白的动规，原理见 wikipedia        for (int k = 1; k < MAX; ++k) {            for (int i = 1; i < MAX; ++i) {                for (int j = 1; j < MAX; ++j) {                    if (countries[i][k] + countries[k][j] < countries[i][j]) {                        countries[i][j] = countries[i][k] + countries[k][j];                    }                }            }        }        scanf("%d", &n);        printf("Test Set #%d\n", c++);        int s, e;        while (n--) {            scanf("%d%d", &s, &e);            printf("%d to %d: %d\n", s, e, countries[s][e]);        }        printf("\n");    }    return 0;}