【模板】A*算法（K短路问题）

介绍

模板题：POJ-2449

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
#define maxm 2000000
#define maxn 10000
using namespace std;

struct edge{
    int v,w;
    int next;
}e[maxm], e2[maxm];
int cnt = 0, k;
int head[maxn],head2[maxn];
int dis[maxn], vis[maxn];

struct node{
    int u, w, f;
    bool operator <(const node a) const{
        if(a.f==f)
            return a.w < w;
        return a.f < f;
    }
};

void addedge(int u, int v, int w)
{
    e[cnt].v = v;
    e[cnt].w = w;
    e[cnt].next = head[u];
    head[u] = cnt;
    e2[cnt].v = u;
    e2[cnt].w = w;
    e2[cnt].next = head2[v];
    head2[v] = cnt++;
}


void spfa(int t)
{
    memset(dis, 0x3f, sizeof dis);
    dis[t] = 0;
    int inq[maxn];
    memset(inq, 0, sizeof inq);
    queue<int> q;
    q.push(t);
    inq[t] = 1;
    while(!q.empty())
    {
        int x = q.front();
        q.pop(); inq[x] = 0;
        for(int i=head2[x];i!=-1;i=e2[i].next)
        {
            if(dis[x]+e2[i].w < dis[e2[i].v])
            {
                dis[e2[i].v] = dis[x]+e2[i].w;
                if(!inq[e2[i].v]){
                    q.push(e2[i].v);
                    inq[e2[i].v] = 1;
                }
            }
        }
    }
}


int a_star(int s, int t)
{
    priority_queue<node> q;
    if(s==t) k++;
    if(dis[s]==0x3f3f3f3f) return -1;
    q.push(node{s, 0, 0+dis[s]});
    int kcnt = 0;
    while(!q.empty())
    {
        int u = q.top().u, w = q.top().w;
        if(u==t)
        {
           kcnt++;
           if(kcnt==k){
               return w;
           }
        }
        q.pop();
        for(int i=head[u];i!=-1;i=e[i].next)
        {
            q.push(node{e[i].v, w+e[i].w, w+e[i].w+dis[e[i].v]});
        }
    }
    return -1;
}


int main()
{
    int m,n, u, v, w, s, t;
    while(cin >> n >> m){
        memset(head, -1, sizeof head);
        memset(head2, -1, sizeof head2);
        for(int i=0;i<m;i++)
        {
            scanf("%d %d %d", &u,&v,&w);
            addedge(u, v, w);
        }
        scanf("%d %d %d",&s, &t, &k);
        spfa(t);
        cout << a_star(s, t) << endl;
    }
    
    return 0;
}