(bfs) acwing 847. Hierarchy of points in the graph

847. The hierarchy of dots in the graph

Topic link https://www.acwing.com/problem/content/849/
subject ：

Ideas ： The number of points like this is very large , You can think about it bfs Can we solve , because bfs The complexity of is the number of edges

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int N=1e5+10;
int h[N],e[N],ne[N],idx;
int dis[N];
int n,m;
void add(int x,int y){
    
    e[idx]=y,ne[idx]=h[x],h[x]=idx++;
}
void bfs(){
    
    dis[1]=0;
    queue<int > q;
    q.push(1);
    while(q.size()){
    
        int u=q.front();
        q.pop();
        for(int i=h[u];i!=-1;i=ne[i]){
    
            int t=e[i];
            if(!dis[t]){
    
                dis[t]=dis[u]+1;
                q.push(t);
            }

        }
    }
}
int main(){
    
    cin>>n>>m;
    int x,y;
    memset(h,-1,sizeof h);
    for(int i=0;i<m;i++){
    
        scanf("%d%d",&x,&y);
        add(x,y);
    }
    bfs();
    if(n==1){
    
        cout<<0;
    }else{
    
        if(dis[n]==0){
    
            cout<<-1;
        }else{
    
            cout<<dis[n];
        }
    }
    return 0;
}