HDU 3760(最短路思路)

先倒着从n bfs一遍求出bfs树每层的节点，然后从1贪心的走回来就行了

这个贪心用两个queue即可实现。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
#define rep(i , n) for(int i = 0 ;i<(int)n;i++)
#define rep1(i,x,y) for(int i = (int)x ; i<=(int)y;i++)

const int N = 1e5 + 100;
const int M = 4e5 + 100;
struct node{
   int u , v , c;
   node(int u = 0 ,int v = 0 , int c = 0):u(u),v(v),c(c){}
}e[M];
int head[N] , nex[M] , cnt ;
int n, m;
void init(){
    cnt = 0;
    rep1(i,1,n) head[i] = -1;
}
void add_edge(int u ,int v , int c){
     e[++cnt] = node(u , v , c);
     nex[cnt] = head[u];
     head[u] = cnt;
}
int d[N];
void bfs(){
    int q[N] , front = 0, rear = 0;
    rep1(i , 1 , n) d[i] = -1;
    d[n] = 0;
    q[front] = n;
    while(front <= rear){
         int u = q[front++];
         for(int i = head[u] ; i!= -1 ; i = nex[i]){
              node te = e[i];
              if(d[te.v] == -1){
                   d[te.v] = 1 + d[u];
                   q[++rear]  = te.v;
              }
         }
    }
}
int ans[N] , done[N];
void bfs2(){
    queue<int> q[3];
    rep1(i ,1 , n) done[i] = -1;
    int now = 0, pre = 1;
    q[pre].push(1);
    int  flag= 0;
    while(d[q[pre].front()] > 0){
         ++flag;
         int min_ = 1e9 + 100;
         while(!q[pre].empty()){
              int u = q[pre].front(); q[pre].pop();
              for(int i = head[u] ; i!=-1 ; i = nex[i]){
                     node te = e[i];
                     if(d[te.v] + 1 != d[u]) continue;
                     if(te.c > min_) continue;
                     if(te.c < min_){
                        while(!q[2].empty()) q[2].pop();
                        min_ = te.c;
                     }
                     q[2].push(te.v);
              }
         }
         while(!q[2].empty()){
              int u = q[2].front(); q[2].pop();
              if(done[u] != flag){
                    done[u] = flag;
                    q[now].push(u);
              }
         }
         swap(pre, now);
         ans[flag] = min_;
    }
    printf("%d\n",d[1]);
    for(int i = 1 ; i<=flag ;  i++){
           if(i > 1) printf(" ");
           printf("%d",ans[i]);
    }  printf("\n");
}
int main()
{
   int T;
   scanf("%d",&T);
   while(T--){
       scanf("%d %d",&n,&m);
       init();
       rep(i,m){
          int u , v, c;
          scanf("%d %d %d",&u,&v,&c);
          add_edge(u , v , c);
          add_edge(v , u , c);
       }
       bfs();
       bfs2();
   }
   return 0;
}