图中点的层次

代码

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int h[N],e[N],ne[N],idx,d[N],n,m;
void add(int a,int b){
    e[idx] = b,ne[idx] = h[a],h[a] = idx ++;
}
int bfs(){
    memset(d,-1,sizeof d);
    d[1] = 0;
    queue<int> q;
    q.push(1);
    while(!q.empty()){
        int t = q.front();
        q.pop();
        for(int i = h[t]; ~i; i = ne[i]){
            int j = e[i];
            if(d[j] == -1){
                d[j] = d[t] + 1;
                q.push(j);
            }
        }
    }
    return d[n];
}
int main(){
    memset(h, -1, sizeof h);
    cin >> n >> m;
    while(m --){
        int a,b;
        cin >> a >> b;
        add(a,b);
    }
    cout << bfs() << endl;
    return 0;
}