图论 k短路

用到A*

推两篇博客

https://blog.csdn.net/Z_Mendez/article/details/47057461

https://blog.csdn.net/v_july_v/article/details/6177380

板子

#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
#include<set>
#include<string>
using namespace std;
const int INF=0x3f3f3f3f;
typedef pair<int, int> pr;
typedef long long ll;
#define fi first
#define se second
#define me(x) memset(x, -1, sizeof(x))
#define mem(x) memset(x, 0, sizeof(x))
#define N 20000+5
#define NIL -1
struct edg
{
    int next, to, w;
}edge[N], edge1[N];
struct node
{
    int p, h, g;
    bool operator<(node x) const
    {
        return x.g+x.h<g+h;
    }
};
int cnt, cnt1, n, m, k;
int head[N], head1[N], dist[N], vis[N], t[N];
struct cmp
{
    bool operator()(const int &a, const int &b) const
    {
        return dist[a]<dist[b] || (dist[a]==dist[b]&&a<b);
    }
};
set<int,cmp> s;
void init()
{
    s.clear();
    cnt=0;
    cnt1=0;
    me(head);
    mem(vis);
    me(head1);
    mem(t);
    for(int i=1; i<=n; i++)
        dist[i]=INF;
}
void add(int u, int v, int w)
{
    edge[cnt].w=w;
    edge[cnt].to=v;
    edge[cnt].next=head[u];
    head[u]=cnt++;
}

void add1(int u, int v, int w)
{
    edge1[cnt1].w=w;
    edge1[cnt1].to=v;
    edge1[cnt1].next=head1[u];
    head1[u]=cnt1++;
}
void dijkstra(int z)
{
    s.insert(z);
    dist[z]=0;
    while(s.size())
    {
        int v=*s.begin();
        s.erase(v);
        vis[v]=1;
        for(int i=head1[v]; ~i; i=edge1[i].next)
        {
            int t=edge1[i].to;
            if(!vis[t] && dist[t]>dist[v]+edge1[i].w)
            {
                s.erase(t);
                dist[t]=dist[v]+edge1[i].w;
                s.insert(t);
            }
        }
    }
}
priority_queue<node> que;

int astar(int s, int e)
{
    node x, y;
    x.g=0; x.h=0; x.p=s;
    que.push(x);
    while(que.size())
    {
        x=que.top();
        que.pop();
        t[x.p]++;
        if(t[x.p]==k && x.p==e) return x.h+x.g;
        if(t[x.p]>k) continue;
        for(int i=head[x.p]; ~i; i=edge[i].next)
        {
            y.p=edge[i].to;
            y.g=dist[edge[i].to];
            y.h=edge[i].w+x.h;
            que.push(y);
        }
    }
    return -1;
}
int main()
{
    int i, j, z;
    int x, y, u, v, w;
    while(cin>>n>>m)
    {
        init();
        for(i=0; i<m; i++)
            cin>>u>>v>>w, add(u, v, w), add1(v, u, w);
        cin>>x>>y>>k;
        dijkstra(y);
        z=astar(x, y);
        cout<<z<<endl;
    }
}