https://www.acmicpc.net/problem/24446
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <ext/rope>
#define fastio ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
using namespace std;
using namespace __gnu_cxx;
#define X first
#define Y second
#define int int64_t
#define sz(v) (int)(v).size()
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define Compress(v) sort(all(v)), (v).erase(unique(all(v)), (v).end())
#define OOB(x, y) ((x) < 0 || (x) >= n || (y) < 0 || (y) >= m)
#define IDX(v, x) (lower_bound(all(v), x) - (v).begin())
#define debug(x) cout << (#x) << ": " << (x) << '\n'
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using tii = tuple<int, int, int>;
template <typename T>
using wector = vector<vector<T>>;
vector<int> adj[100001];
int n, m, r;
vector<int> bfs(int st)
{
vector<int> dist(n + 1, -1);
queue<int> Q;
dist[st] = 0;
Q.push(st);
while (!Q.empty())
{
auto cur = Q.front();
Q.pop();
for (auto &nxt : adj[cur])
{
if (nxt < 1 || nxt > n || dist[nxt] != -1)
continue;
dist[nxt] = dist[cur] + 1;
Q.push(nxt);
}
}
return dist;
}
int32_t main()
{
fastio;
cin >> n >> m >> r;
for (int i = 0; i < m; i++)
{
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
auto dist = bfs(r);
for (int i = 1; i <= n; i++)
cout << (dist[i] == -1 ? -1 : dist[i]) << "\n";
}
그냥 BFS를 돌려주면 됩니다.