Linhas de Ônibus

#include<iostream>
#include<queue>
#include<vector>
#include<string.h>
using namespace std;


const int N = 6e2;
vector<int> graph[2*N];
int father[2*N];
bool viz[2*N];
int T, L, O, D, C, x;

void BFS(int O){
    memset(father, -1, sizeof(father));
    memset(viz, false, sizeof(viz));
    int at, neighbor;
    queue<int> q;
    q.push(O);
    while(q.size()){
        at = q.front();
        viz[at] = true;
        q.pop();
        for(int i=0; i < graph[at].size(); i++){
            neighbor = graph[at][i];
            if(!viz[neighbor]){
                q.push(neighbor);
                father[neighbor] = at;
            }
        }
    }
}

int solve(int O, int D){
    int at = D;
    int qtd = 0;
    while(father[at] != O){
        at = father[at];
        qtd++;
    }
    return qtd;
}


int main(){
    cin >> T >> L >> O >> D;
    for(int i=0; i < L; i++){
        cin >> C;
        for(int j=0; j < C; j++){
            cin >> x;
            graph[N+i].push_back(x);
            graph[x].push_back(N+i);
        }
    }
    BFS(O);

    cout << 1 + solve(O, D)/2 << endl;
}