UVa 11374 机场快线

https://vjudge.net/problem/UVA-11374

题意：

机场快线分为经济线和商业线两种，线路、速度和价格都不同。你有一张商业线车票，可以坐一站商业线，而其他时候只能乘坐经济线。你的任务是找一条去机场最快的线路。

思路：

因为商业线只能坐一站，所有可以枚举坐的是哪一站，用dijkstra算出起点到每个点的最短时间f(x)和终点到每个点的最短时间g(x)，则总时间为f(a)+T(a,b)+g(b)，其中T（a，b）为从a坐一站商业线到达b的时间。

 #include <iostream>
 #include <cstring>
 #include <algorithm>
 #include <vector>
 #include <queue>
 using namespace std;

 const int INF = ;
 const int maxn =  + ;

 struct Edge
 {
     int from, to, dist;
     Edge(int u, int v, int d) :from(u), to(v), dist(d){}
 };

 struct HeapNode
 {
     int d, u;
     HeapNode(int x, int y) :d(x), u(y){}
     bool operator < (const HeapNode& rhs) const{
         return d > rhs.d;
     }
 };

 struct Dijkstra
 {
     int n, m;                  //点数和边数
     vector<Edge> edges;        //边列表
     vector<int> G[maxn];       //每个结点出发的边编号（从0开始编号）
     bool done[maxn];           //是否已永久标号
     int d[maxn];               //s到各个点的距离
     int p[maxn];               //最短路中的上一条边

     void init(int n)
     {
         this->n = n;
         for (int i = ; i < n; i++)    G[i].clear();
         edges.clear();
     }

     void AddEdges(int from, int to, int dist)
     {
         edges.push_back(Edge(from,to,dist));
         m = edges.size();
         G[from].push_back((m - ));
     }

     void dijkstra(int s)
     {
         priority_queue<HeapNode> Q;
         for (int i = ; i < n; i++)    d[i] = INF;
         d[s] = ;
         memset(done, , sizeof(done));
         Q.push(HeapNode(,s));
         while (!Q.empty())
         {
             HeapNode x = Q.top(); Q.pop();
             int u = x.u;
             if (done[u]) continue;
             done[u] = true;
             for (int i = ; i < G[u].size(); i++)
             {
                 Edge& e = edges[G[u][i]];
                 if (d[e.to] > d[u] + e.dist)
                 {
                     d[e.to] = d[u] + e.dist;
                     p[e.to] = e.from;
                     Q.push(HeapNode(d[e.to],e.to));
                 }
             }
         }
     }

     void getpath(int s, int e, vector<int>& path)
     {
         int pos = e;
         while (true)
         {
             path.push_back(pos);
             if (pos == s)
                 break;
             pos = p[pos];
         }
     }

 }t[];

 int N, S, E;
 vector<int> path;

 int main()
 {
     //freopen("D:\\input.txt", "r", stdin);
     int time, kase = ;
     while (scanf("%d%d%d", &N, &S, &E) != EOF)
     {
         S--; E--;
         if (kase != )   printf("\n");
         kase++;
         t[].init(N);
         t[].init(N);
         path.clear();
         int M, K;
         int u, v, d;
         scanf("%d", &M);
         while (M--)
         {
             scanf("%d%d%d", &u, &v, &d);
             u--; v--;
             t[].AddEdges(u, v, d);
             t[].AddEdges(u, v, d);
             t[].AddEdges(v, u, d);
             t[].AddEdges(v, u, d);
         }
         t[].dijkstra(S);
         t[].dijkstra(E);
         int ks = -, ke = -;
         time = t[].d[E];
         scanf("%d", &K);
         while (K--)
         {
             scanf("%d%d%d", &u, &v, &d);
             u--;v--;
             if (d + t[].d[u] + t[].d[v] < time){
                 time = d + t[].d[u] + t[].d[v];
                 ks = u; ke = v;
             }
             if (d + t[].d[v] + t[].d[u] < time){
                 time = d + t[].d[v] + t[].d[u];
                 ks = v; ke = u;
             }
         }
         if (ks == -)
         {
             t[].getpath(S, E, path);
             reverse(path.begin(), path.end());
             for (int i = ; i < path.size() - ; i++)
                 printf("%d ", path[i]+);
             printf("%d\n", E+);
             printf("Ticket Not Used\n");
             printf("%d\n", time);
         }
         else
         {
             t[].getpath(S, ks, path);
             reverse(path.begin(), path.end());
             t[].getpath(E, ke, path);
             for (int i = ; i < path.size() - ; i++)
                 printf("%d ", path[i]+ );
             printf("%d\n", E+);
             printf("%d\n", ks + );
             printf("%d\n", time);
         }
     }
     return ;
 }