Distante

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

ifstream fin("distante.in");
ofstream fout("distante.out");

int n , m , A[1001][1001], V[1001], Dp[1001], Dq[1001], p , q;

void BFS(int x , int D[])
{
    for(int i = 1 ; i <= n ; i ++)
        V[i] = 0;
    int Q[1001], st = 1 , dr = 0;
    Q[++dr] = x, V[x]  = 1, D[x] = 0;
    while(st <= dr)
    {
        int k = Q[st];
        for(int i = 1 ; i <= n ; i ++)
            if(A[k][i] == 1 && V[i] == 0)
            {
                Q[++ dr] = i;
                V[i] = 1;
                D[i] = D[k] + 1;
            }
        st ++;
    }
}

int main()
{
    int i , j;
    fin >> n >> m >> p >> q;
    while(m)
    {
        fin >> i >> j;
        A[i][j] = A[j][i] = 1;
        m --;
    }
    BFS(p, Dp);
    BFS(q, Dq);
    for(int i = 1 ; i <= n ; i ++)
        if(Dp[i] == Dq[i])
            fout << i << " ";
    fout << '\n';
    return 0;
}