bzoj 2763 [JLOI2011]飞行路线 Dijikstra 分层

k<=10，所以每用一次机会就跳到一个新图中，

每一个图按原图建边，相邻两图中建边权为0的边

补一补dj，好像我以前觉得dj特别难，hhhhh

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<iostream>
#define N 500500
using namespace std;
int n,m,k,S,T;
struct point{
    int st,dis;
    bool operator < (const point &a)const{
        return dis>a.dis;
    }
}p[N];
int e=1,head[N],dis[N];
bool bo[N];
struct edge{
    int u,v,w,next;
}ed[5000500];
void add(int u,int v,int w){
    ed[e].u=u; ed[e].v=v; ed[e].w=w;
    ed[e].next=head[u]; head[u]=e++;
}
priority_queue<point> q;
int dijkstra(){
    memset(dis,0x7f,sizeof dis);
    memset(bo,0,sizeof bo);
    dis[S]=0;q.push((point){S,0});
    while(!q.empty()){
        point now=q.top();q.pop();
        if(bo[now.st]) continue;
        bo[now.st]=1;
        for(int i=head[now.st];i;i=ed[i].next)
            if(dis[now.st]+ed[i].w<dis[ed[i].v]){
                dis[ed[i].v]=dis[now.st]+ed[i].w;
                q.push((point){ed[i].v,dis[ed[i].v]});
            }
    }
    int ans=0x7fffffff;
    for(int i=0;i<=k;i++)
        ans=min(ans,dis[i*n+T]);
    return ans;

}
int main(){
    scanf("%d%d%d",&n,&m,&k);
    scanf("%d%d",&S,&T);S++;T++;
    int u,v,w;
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&u,&v,&w);
        u++;v++;
        for(int j=0;j<=k;j++){
            add(j*n+u,j*n+v,w),add(j*n+v,j*n+u,w);
            if(j<k)add(j*n+u,(j+1)*n+v,0),add(j*n+v,(j+1)*n+u,0);
        }
    }
    int ans=dijkstra();
    printf("%d\n",ans);
    return 0;
}