POJ——T 2449 Remmarguts' Date

 1 #include <algorithm>
 2 #include <iostream>
 3 #include <cstring>
 4 #include <cstdio>
 5 #include <queue>
 6 
 7 using namespace std;
 8 
 9 const int INF(0x3f3f3f3f);
10 const int M(100005);
11 const int N(1005);
12 int n,m,s,t,k;
13 int sumedge,had[N],hed[N];
14 struct Edge
15 {
16     int v,next,w;
17 }edge1[M<<1],edge2[M<<1];
18 inline void ins(int u,int v,int w)
19 {
20     edge1[++sumedge].v=v;
21     edge1[sumedge].next=hed[u];
22     edge1[sumedge].w=w;
23     hed[u]=sumedge;
24     edge2[sumedge].v=u;
25     edge2[sumedge].next=had[v];
26     edge2[sumedge].w=w;
27     had[v]=sumedge;
28     
29 }
30 
31 int dis[N];
32 bool inq[N];
33 void  SPFA(int s)
34 {
35     for(int i=1;i<=n;i++) dis[i]=INF;
36     queue<int>que; que.push(s);
37     inq[s]=true; dis[s]=0;
38     for(;!que.empty();)
39     {
40         int u=que.front();
41         que.pop(); inq[u]=0;
42         for(int v,i=had[u];i;i=edge2[i].next)
43         {
44             v=edge2[i].v;
45             if(dis[v]>dis[u]+edge2[i].w)
46             {
47                 dis[v]=dis[u]+edge2[i].w;
48                 if(!inq[v]) que.push(v),inq[v]=1;
49             }
50         }
51     }
52 }
53 
54 struct Node
55 {
56     int g,f,to;
57     bool operator < (const Node x) const
58     {
59         if(f==x.f) return g>x.g;
60         return f>x.f;
61     }
62 };
63 int Astar()
64 {
65     priority_queue<Node>que;
66     if(dis[s]==INF) return -1;
67     int cnt=0; Node now,v;
68     now.f=dis[s];now.g=0;now.to=s;
69     que.push(now);
70     for(;!que.empty();)
71     {
72         now=que.top(); que.pop();
73         if(now.to==t) cnt++;
74         if(cnt==k) return now.g;
75         for(int i=hed[now.to];i;i=edge1[i].next)
76         {
77              v.to=edge1[i].v;
78             v.g=now.g+edge1[i].w;
79             v.f=v.g+dis[edge1[i].v];
80             que.push(v);
81         }
82     }
83     return -1;
84 }
85 
86 int main()
87 {
88     scanf("%d%d",&n,&m);
89     for(int u,v,w;m--;)
90     {
91         scanf("%d%d%d",&u,&v,&w);
92         ins(u,v,w);
93     }
94     scanf("%d%d%d",&s,&t,&k);
95     if(s==t) k++; SPFA(t);
96     printf("%d\n",Astar());
97     return 0;
98 }