бфс

#include <algorithm>
#include <iostream>
#include <map>
#include <vector>
#include <algorithm>
#include <unordered_set>
#include <set>
#include <deque>

using namespace std;

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

    return 0;
}