【图论】【A*搜索】[POJ2449]Remmarguts' Date

题目
本题实质是求第k短的路径；
SPFA+A*
进行启发式搜索直至访问终点k次，
估值函数：当前已经走的距离+当前点到终点的最短路
注意：当s==t时，要特判

#include<cstdio>
#include<queue>
#include<cstring>
#include<cstdlib>
using namespace std;
#define MAXN 1000
#define MAXM 100000
queue<int>q;
struct node2{
    int pos,d,f;
    bool operator < (const node2 &x) const{
        return f>x.f;
    }
};
priority_queue<node2>pq;
int n,m,dist[MAXN+10],s,t,k;
bool vis[MAXN+10];
struct node{
    int u,v,wt;
    node *next;
}edge[MAXM*2+10],*adj[MAXN+10],*adj2[MAXN+10],*ecnt=&edge[0];
void Read(int &x){
    char c;
    while((c=getchar())&&c!=EOF)
        if(c>='0'&&c<='9'){
            x=c-'0';
            while((c=getchar())&&c>='0'&&c<='9')
                x=x*10+c-'0';
            ungetc(c,stdin);
            return;
        }
}
void addedge(int u,int v,int wt){
    node *p=++ecnt;
    p->v=v;
    p->wt=wt;
    p->next=adj[u];
    adj[u]=p;
}
void addedge2(int u,int v,int wt){
    node *p=++ecnt;
    p->v=v;
    p->wt=wt;
    p->next=adj2[u];
    adj2[u]=p;
}
void read(){
    Read(n),Read(m);
    int i,u,v,wt;
    for(i=1;i<=m;i++){
        Read(u),Read(v),Read(wt);
        addedge(u,v,wt);
        addedge2(v,u,wt);
    }
    Read(s),Read(t),Read(k);
    if(s==t)
        k++;
}
void spfa(int s){
    q.push(s);
    dist[s]=0;
    vis[s]=1;
    int u,v,wt;
    while(!q.empty()){
        u=q.front();
        q.pop();
        vis[u]=0;
        for(node *p=adj2[u];p;p=p->next){
            v=p->v,wt=p->wt;
            if(dist[v]>dist[u]+wt){
                dist[v]=dist[u]+wt;
                if(!vis[v]){
                    q.push(v);
                    vis[v]=1;
                }
            }
        }
    }
}
void Astar(){
    node2 u,v;
    int cnt=0;
    u.pos=s,u.d=0,u.f=dist[s];
    pq.push(u);
    while(!pq.empty()){
        u=pq.top();
        if(u.pos==t)
            cnt++;
        if(cnt==k){
            printf("%d",u.d);
            exit(0);
        }
        pq.pop();
        for(node *p=adj[u.pos];p;p=p->next){
            v.pos=p->v;
            v.d=p->wt+u.d;
            v.f=v.d+dist[p->v];
            pq.push(v);
        }
    }
}
int main()
{
    memset(dist,0x7f,sizeof dist);
    read();
    spfa(t);
    Astar();
    printf("-1");
}