K短路 spfa + A*

 #include <stdio.h>
 #include <string.h>
 #include <queue>
 #include <algorithm>
 using namespace std;
 const int L = ;
 const int inf = <<;
 struct node
 {
     int now,g,f;
     bool operator <(const node a)const
     {
         if(a.f == f) return a.g < g;
         return a.f < f;
     }
 };
 struct edges
 {
     int x,y,w,next;
 } e[L<<],re[L<<];//e是输入给出的定向图，re为其逆向图，用于求t到其他所有点的最短路径

 int head[],dis[],vis[],n,m,k,s,t,rehead[];

 void Init()//初始化
 {
     memset(e,-,sizeof(e));
     memset(re,-,sizeof(re));
     for(int i = ; i<=n; i++)
     {
         dis[i] = inf;
         vis[i] = ;
         head[i] = -;
         rehead[i] = -;
     }
 }

 void AddEdges(int x,int y,int w,int k)
 {
     e[k].x = x,e[k].y = y,e[k].w = w,e[k].next = head[x],head[x] = k;
     re[k].x = y,re[k].y = x,re[k].w = w,re[k].next = rehead[y],rehead[y] = k;
 }

 int relax(int u,int v,int c)
 {
     if(dis[v]>dis[u]+c)
     {
         dis[v] = dis[u]+c;
         return ;
     }
     return ;
 }

 void SPFA(int src)
 {
     int i;
     dis[src] = ;
     queue<int> Q;
     Q.push(src);
     while(!Q.empty())
     {
         int u,v;
         u = Q.front();
         Q.pop();
         vis[u] = ;
         for(i = rehead[u]; i!=-; i = re[i].next)
         {
             v = re[i].y;
             if(relax(u,v,re[i].w) && !vis[v])
             {
                 Q.push(v);
                 vis[v] = ;
             }
         }
     }
 }

 int Astar(int src,int to)
 {
     priority_queue<node> Q;
     int i,cnt = ;
     if(src == to) k++;//在起点与终点是同一点的情况下，k要+1
     if(dis[src] == inf) return -;
     node a,next;
     a.now = src;
     a.g = ;
     a.f = dis[src];
     Q.push(a);
     while(!Q.empty())
     {
         a = Q.top();
         Q.pop();
         if(a.now == to)
         {
             cnt++;
             if(cnt == k)
                 return a.g;
         }
         for(i = head[a.now]; i!=-; i = e[i].next)
         {
             next = a;
             next.now = e[i].y;
             next.g = a.g+e[i].w;
             next.f = next.g+dis[next.now];
             Q.push(next);

         }
     }
     return -;
 }

 int main()
 {
     int i,j,x,y,w;
     while(~scanf("%d%d",&n,&m))
     {
         Init();
         for(i = ; i<m; i++)
         {
             scanf("%d%d%d",&x,&y,&w);
             AddEdges(x,y,w,i);
         }
         scanf("%d%d%d",&s,&t,&k);
         SPFA(t);
         printf("%d\n",Astar(s,t));
     }

     return ;
 }