POJ3967Ideal Path[反向bfs 层次图]

//
//  main.cpp
//  poj3967
//
//  Created by Candy on 9/25/16.
//  Copyright © 2016 Candy. All rights reserved.
//

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
const int N=1e5+5,M=2e5+5,INF=1e9+5;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}
    return x;
}
int n,m,u,v,w;
struct edge{
    int v,w,ne;
}e[M<<1];
int h[N],cnt=0;
inline void ins(int u,int v,int w){
    cnt++;
    e[cnt].v=v;e[cnt].w=w;e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].w=w;e[cnt].ne=h[v];h[v]=cnt;
}
int vis[N],q[N],head=1,tail=0;
int d[N];
void bfs1(){
    q[++tail]=n;vis[n]=1;
    d[n]=1;
    while(head<=tail){
        int u=q[head++];
        for(int i=h[u];i;i=e[i].ne){
            int v=e[i].v;
            if(vis[v]) continue;
            vis[v]=1;
            d[v]=d[u]+1;
            q[++tail]=v;
        }
    }
}
int ans[N],lst[N],num=0;
void bfs2(){
    memset(ans,127,sizeof(ans));
    head=1;tail=0;
    memset(q,0,sizeof(q));
    memset(vis,0,sizeof(vis));
    q[++tail]=1;
    while(head<=tail||num>=1){
        int mn=INF,dis=0;num=0;
        while(head<=tail){
            int u=q[head++];dis=d[u]; //printf("u %d\n",u);
            for(int i=h[u];i;i=e[i].ne){
                int v=e[i].v,c=e[i].w;
                if(d[v]!=d[u]-1) continue;
                if(c>mn) continue;
                if(c<mn){
                    num=0; mn=c;
                    lst[++num]=v;
                }else lst[++num]=v;
            }
        }
        ans[dis]=mn;
        for(int i=1;i<=num;i++)
            if(!vis[lst[i]]){vis[lst[i]]=1;q[++tail]=lst[i];}
    }
}
int main(int argc, const char * argv[]) {
    n=read();m=read();
    for(int i=1;i<=m;i++){
        u=read();v=read();w=read();
        if(u!=v) ins(u,v,w);
    }
    bfs1();
    bfs2();
    printf("%d\n",d[1]-1);
    for(int i=d[1];i>1;i--) printf("%d ",ans[i]);
  //  cout<<"\n\n";
  //  for(int i=1;i<=n;i++) printf("%d ",d[i]);
    return 0;
}