bfs

#include "bits/stdc++.h"

using namespace std;

const int maxN = 100;
bool visited[maxN];
int cost[maxN];
vector<int> adj[maxN];

void bfs (int source) {
	queue<int> q;
	q.push(source);
	cost[source] = 0;
	visited[source] = true;
	while (!q.empty()) {
		int u = q.front();
		q.pop();
		for (int v : adj[u]) {
			if (!visited[v]) {
				cost[v] = cost[u] + 1;
				visited[v] = true;
				q.push(v);
			}
		}
	}
}

int main () {
	 int n = 5, m = 5;
	 for (int i = 1; i <= m; ++i) {
		 int u, v;
		 cin >> u >> v;
		 adj[u].push_back(v);
		 adj[v].push_back(u);
	 }
	 bfs(1);
	 for (int i = 1; i <= n; ++i) cout << cost[i] << ' ';
}