2368.cpp

class Solution {
  public:
    int reachableNodes(int n, vector<vector<int>> &edges, vector<int> &restricted) {
        unordered_set<int> rest(restricted.begin(), restricted.end());
        vector<vector<int>> adj(n, vector<int>());

        for (auto &p : edges) {
            if (rest.count(p[0]) || rest.count(p[1])) continue;
            adj[p[0]].push_back(p[1]);
            adj[p[1]].push_back(p[0]);
        }

        int res = 0;
        stack<int> st;
        vector<bool> visited(n, false);
        st.push(0);
        visited[0] = true;
        while (!st.empty()) {
            int root = st.top();
            st.pop();
            res++;
            for (int c : adj[root])
                if (!visited[c]) {
                    st.push(c);
                    visited[c] = true;
                }
        }
        return res;
    }
};