python/TangDou/AcWing/GraphBfs/847.cpp

#include <bits/stdc++.h>

using namespace std;
const int N = 100010, M = N << 1;
int n, m;

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

int d[N];

int bfs() {
    queue<int> q;
    q.push(1);
    d[1] = 0;
    while (q.size()) {
        auto u = q.front();
        q.pop();
        for (int i = h[u]; ~i; i = ne[i]) {
            int j = e[i];
            if (d[j] == -1) {
                d[j] = d[u] + 1;
                q.push(j);
            }
        }
    }
    return d[n];
}

int main() {
    memset(h, -1, sizeof h);
    memset(d, -1, sizeof d);
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }
    cout << bfs() << endl;
    return 0;
}