BFS

#include <iostream>
#include <set>
#include <vector>
#include <deque>

using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector < vector<int>>g(n);
    int x, y;
    for (int i = 0;i < m;i++)
    {
        cin >> x >> y;
        g[x - 1].push_back(y - 1);
        g[y - 1].push_back(x - 1);
    }
    deque<int> q;
    vector<bool> used(n, false);
    vector<int> answ(n, 0);
    int start;
    cin >> start;
    start--;
    q.push_back(start);
    used[start] = true;
    while (!q.empty()) {
        int cur = q.front();
        q.pop_front();
        for (auto nxt : g[cur]) {
            if (!used[nxt]) {
                answ[nxt] = answ[cur] + 1;
                used[nxt] = true;
                q.push_back(nxt);
            }
        }
    }
    for (auto e : answ) cout << e << ' ';
    return 0;
}