getline与stringstream的用法

https://www.acwing.com/problem/content/922/

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

const int N = 505;

int n, m;
int dist[N], stop[N], q[N];
bool g[N][N];

void bfs() {
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    int hh = 0, tt = 0;
    q[0] = 1;

    while (hh <= tt) {
        auto t = q[hh ++];

        for (int i = 1; i <= n; i ++)
            if (g[t][i] && dist[i] > dist[t] + 1) {
                dist[i] = dist[t] + 1;
                q[++ tt] = i;
            }
    }
}

int main() {
    cin >> m >> n;
    
    string str;
    getline(cin, str);
    while (m --) {
        getline(cin, str);
        stringstream ssin(str);
        int cnt = 0, p;
        while (ssin >> p) stop[cnt ++] = p;

        for (int i = 0; i < cnt; i ++)
            for (int j = i + 1; j < cnt; j ++)
                g[stop[i]][stop[j]] = true;
    }

    bfs();

    if (dist[n] == 0x3f3f3f3f) cout << "NO" << endl;
    else cout << max(dist[n] - 1, 0) << endl;
    return 0;
}