BOJ 23887 프린트 전달

void solve(){
    int N, M, K; cin >> N >> M >> K;
    vector<vector<int>> board(N, vector<int>(M, 0));
    vector<pii> students(K+1);
    vector<bool> visited(K+1);
    rep(i, 1, K+1){
        int x, y; cin >> x >> y;
        x--; y--;
        students[i] = {x, y};
        board[x][y] = i;
    }
    int S; cin >> S;
    set<int> Q;
    Q.insert(S);
    visited[S] = true;

    vector<vector<int>> links(K+1);

    vector<int> dx = {-1, -1, -1, 0, 0, 1, 1, 1};
    vector<int> dy = {-1, 0, 1, -1, 1, -1, 0, 1};
    while(!Q.empty()){
        set<int> nQ;
        for(auto cur: Q){
            auto [cx, cy] = students[cur];
            rep(d, 0, 8){
                int nx = cx + dx[d];
                int ny = cy + dy[d];
                if(nx < 0 || nx >= N || ny < 0 || ny >= M) continue;
                if(board[nx][ny] == 0) continue;
                int nxt = board[nx][ny];
                if(visited[nxt]) continue;

                visited[nxt] = true;
                links[cur].push_back(nxt);
                nQ.insert(nxt);
            }
        }
        swap(Q, nQ);
    }
    rep(i, 1, K+1) if(!visited[i]){
        cout << -1;
        return;
    }

    vector<int> sz(K+1);
    function<void(int)> dfs = [&](int cur){
        sz[cur] = 1;
        for(auto nxt: links[cur]){
            dfs(nxt);
            sz[cur] += sz[nxt];
        }
    };
    dfs(S);
    rep(i, 1, K+1) cout << sz[i] << ' ';
}