1131（★、※）Subway Map

思路：DFS遍历

 #include <iostream>
 #include <map>
 #include <vector>
 #include <cstdio>
 using namespace std;
 
 const int INF = 0x7fffffff;
 const int maxn = ;
 
 struct Node{
     int line, s, e;
     Node(int xl, int xs, int xe) :line(xl), s(xs), e(xe) {}
 };
 
 struct WhichLine {
     int u, v;
     WhichLine(int _u, int _v) :u(_u), v(_v) {}
     friend bool operator <(WhichLine a,WhichLine b) {//const whichLine &a, const whichLine &b
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　//如果只是whichLine &a, whichLine &b报错
         if (a.u != b.u) return a.u < b.u;
         else return a.v < b.v;
     }
 };
 map<WhichLine, int> searchLine;//判断两个站点在哪条线上
 vector<int> G[maxn];//图的邻接表
 bool visit[maxn];//判断是否已经访问数组
 int minStation, minTransfer;//最少的站点，最少的换乘
 vector<Node> ans, temp;//最终结果路径和中间记录路径
 int st, ed;
 
 void DFS(int head, int now, int stationCnt, int pre) {
     if (now == ed) {
         if (stationCnt < minStation || stationCnt == minStation && temp.size() < minTransfer) {
             minStation = stationCnt;
             minTransfer = temp.size();
             ans = temp;
             ans.push_back(Node(searchLine[WhichLine(pre, now)], head, now));
             return;
         }
     }
 
     visit[now] = true;
     for (auto next : G[now]) {
         if (visit[next]) continue;
         if (pre != now && searchLine[WhichLine(pre, now)] != searchLine[WhichLine(now, next)]) {
 
             temp.push_back(Node(searchLine[WhichLine(pre, now)], head, now));
             DFS(now, next, stationCnt + , now);
             temp.pop_back();
         }
         else DFS(head, next, stationCnt + , now);
     }
 
     visit[now] = false;
 }
 
 int main(){
     int n;
     scanf("%d", &n);
     for (int i = ; i <= n; ++i){
         int k, u, v;
         scanf("%d", &k);
         for (int j = ; j < k; j++) {
             scanf("%d", &v);
             if (j > ) {
                 searchLine[WhichLine(u, v)] = i;//两个相邻节点的线路
                 searchLine[WhichLine(v, u)] = i;
                 G[u].push_back(v);
                 G[v].push_back(u);
             }
             u = v;
         }
     }
     int q;
     scanf("%d", &q);
     while (q--){
         scanf("%d %d", &st, &ed);
         minStation = minTransfer = INF;
         DFS(st, st, , st);
         printf("%d\n", minStation);
         for (auto x : ans) printf("Take Line#%d from %04d to %04d.\n", x.line, x.s, x.e);
     }
     return ;
 }