【图论】【A*搜索】[POJ2449]Remmarguts' Date

来源：互联网发布：sql中in与all的区别编辑：程序博客网时间：2024/05/16 01:54

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 100000queue<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");}

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