图中点的层次

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>

using namespace std;

const int N = 100010;

int n, m;
int h[N], e[N], ne[N], idx;
int d[N];// 保存1号点到各个点的距离

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

int bfs()
{
    memset(d, -1, sizeof d);

    queue<int> q;
    d[1] = 0;
    q.push(1);

    while (q.size())
    {
        int t = q.front();
        q.pop();
        // 循环遍历所有与t相距为1的节点
        for (int i = h[t]; i != -1; i = ne[i]) // ne[i]上的点都是与i节点距离为1的点
        {
            int j = e[i]; // 向外走一步
            if (d[j] == -1) // 如果j没有被遍历过
            {
                d[j] = d[t] + 1; // 因为路径长度都是1，所以直接在上一步的基础上加上1即可
                q.push(j); // 将j加到队列中
            }
        }
    }
    return d[n]; // 返回的d[n]即是节点1到节点n的距离

    
}


int main()
{
    scanf("%d%d", &n, &m);
    memset(h, -1, sizeof h);

    for (int i = 0; i < m; i ++ )
    {
        int a, b;
        scanf("%d%d", &a, &b);
        add(a, b);
    }

    cout << bfs() << endl;

    return 0;
}

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 10;

int n, m;
vector<int> h[N];
int d[N];

int bfs()
{
    memset(d, -1, sizeof d);

    queue<int> q;
    q.push(1);
    d[1] = 0;
    while (q.size())
    {
        int t = q.front();
        q.pop();

        for (auto i: h[t])
        {
            if (d[i] == -1)
            {
                d[i] = d[t] + 1;
                q.push(i);
            }
        }
    }

    return d[n];
}

int main()
{
    scanf ("%d%d", &n, &m);

    for (int i = 0; i < m; i ++ )
    {
        int a, b;
        scanf ("%d%d", &a, &b);
        h[a].push_back(b);
    }

    cout << bfs() << endl;

    return 0;
}