POJ2449:K短路

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
const int MAXN=1005;
const int INF=0x3f3f3f3f;
struct Edge{
    int to,w,next;
}es[100005],rves[100005];
int n,m;
int src,tml,kth;
int head[MAXN],tot;
int rhead[MAXN],rtot;
void addedge(int u,int v,int w)
{
    es[tot].to=v;
    es[tot].w=w;
    es[tot].next=head[u];
    head[u]=tot++;
    
    rves[rtot].to=u;
    rves[rtot].w=w;
    rves[rtot].next=rhead[v];
    rhead[v]=rtot++;
}
int d[MAXN],vis[MAXN];
void spfa(int s)//利用反向边确定估价函数h(x):i到tml的距离 
{
    for(int i=1;i<=n;i++)
    {
        d[i]=INF;
        vis[i]=0;
    }
    queue<int> que;
    que.push(s);
    d[s]=0;
    vis[s]=1;
    while(!que.empty())
    {
        int u=que.front();que.pop();
        vis[u]=0;    
        for(int i=rhead[u];i!=-1;i=rves[i].next)
        {
            Edge e=rves[i];
            if(d[e.to]>d[u]+e.w)
            {
                d[e.to]=d[u]+e.w;
                if(!vis[e.to])
                {
                    vis[e.to]=1;
                    que.push(e.to);
                }
            }
        }
    } 
}
struct Node{
    int nod,g,h;
    Node(){}
    Node(int cnod,int cg,int ch):nod(cnod),g(cg),h(ch){}
    bool operator<(const Node &node) const
    {
        return g+h > node.g+node.h;
    }
};
int astar(int s)
{
    priority_queue<Node> que;
    que.push(Node(s,0,d[s]));//g(x):src到i的距离.h(x):i到tml的距离. 
    while(!que.empty())
    {
        Node now=que.top();que.pop();
        int u=now.nod;
        if(u==tml)
        {
            kth--;
            if(kth==0)    return now.g+now.h;//第k条最短路 
        }
        for(int i=head[u];i!=-1;i=es[i].next)
        {
            Edge e=es[i];
            int g=now.g+e.w;
            int h=d[e.to];
            que.push(Node(e.to,g,h));    
        }
    }
    return -1;
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(head,-1,sizeof(head));
        memset(rhead,-1,sizeof(rhead));
        tot=0;
        rtot=0;
        for(int i=0;i<m;i++)
        {
            int u,v,w;
            scanf("%d%d%d",&u,&v,&w);
            addedge(u,v,w);
        }
        scanf("%d%d%d",&src,&tml,&kth);
        if(src==tml)    kth++;//若src等于tml那么最短路为0,不算 
        spfa(tml);
        printf("%d\n",astar(src));
    }
    
    return 0;
}