poj2449 第k短路

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<vector>
using namespace std;
#define ll long long
const int maxn=1e3+5;
const int INF=1e9;

struct line
{
    int to,w;
    line(int _to,int _w)
    {
        to=_to,w=_w;
    }
};
vector<line>ma1[maxn],ma2[maxn];//ma1为真实的路线，ma2为逆的，为了计算终点到各个点的最短距离

int g[maxn],vis[maxn];//g数组为终点到各个点的最短距离
int n,m,s,t,k,time;
struct node
{
    int x,time;//当前节点走过的距离time + x到终点的距离就是这条路线的距离
    node(int _x,int _time)
    {
        x=_x,time=_time;
    }
    bool operator<(const node &a)const
    {
        return g[x]+time>g[a.x]+a.time;
    }
};
void dij()//为了构造g数组
{
    for(int i=1;i<=n;i++)vis[i]=0,g[i]=1e9;
    g[t]=0;
    for(int i=1;i<=n;i++)
    {
        int inde,mi=1e9+10;
        for(int j=1;j<=n;j++)
        {
            if(vis[j]==0&&mi>g[j])
            {
                mi=g[j];
                inde=j;
            }
        }
        vis[inde]=1;
        for(int j=0;j<ma2[inde].size();j++)
            g[ma2[inde][j].to]=min(g[ma2[inde][j].to],g[inde]+ma2[inde][j].w);
    }
}
int astar()//根据g数组指引“bfs”运动
{
    priority_queue<node>que;
    que.push(node(s,0));
   if(s==t)
        k++;
    while(que.size())
    {
        node now=que.top();
        que.pop();
        if(now.x==t)time++;        //到达终点
        if(time==k)return now.time;
        for(int i=0;i<ma1[now.x].size();i++)
        {
            que.push(node(ma1[now.x][i].to,now.time+ma1[now.x][i].w));
        }
    }
    return -1;
}
int main()
{

    cin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int a,b,c;
        scanf("%d %d %d",&a,&b,&c);
        ma1[a].push_back(line(b,c));
        ma2[b].push_back(line(a,c));
    }
    cin>>s>>t>>k;
    dij();
    cout<<astar()<<endl;;
    return 0;
}