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2368. Reachable Nodes With Restrictions 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  int reachableNodes(int n, vector<vector<int>>& edges,
                     vector<int>& restricted) {
    vector<vector<int>> tree(n);
    vector<bool> seen(n);

    for (const vector<int>& edge : edges) {
      const int u = edge[0];
      const int v = edge[1];
      tree[u].push_back(v);
      tree[v].push_back(u);
    }

    for (const int r : restricted)
      seen[r] = true;

    return dfs(tree, 0, seen);
  }

 private:
  int dfs(const vector<vector<int>>& tree, int u, vector<bool>& seen) {
    if (seen[u])
      return 0;

    seen[u] = true;
    int ans = 1;

    for (const int v : tree[u])
      ans += dfs(tree, v, seen);

    return ans;
  }
};

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class Solution {
  public int reachableNodes(int n, int[][] edges, int[] restricted) {
    List<Integer>[] tree = new List[n];
    boolean[] seen = new boolean[n];

    for (int i = 0; i < n; ++i)
      tree[i] = new ArrayList<>();

    for (int[] edge : edges) {
      final int u = edge[0];
      final int v = edge[1];
      tree[u].add(v);
      tree[v].add(u);
    }

    for (final int r : restricted)
      seen[r] = true;

    return dfs(tree, 0, seen);
  }

  private int dfs(List<Integer>[] tree, int u, boolean[] seen) {
    if (seen[u])
      return 0;

    seen[u] = true;
    int ans = 1;

    for (final int v : tree[u])
      ans += dfs(tree, v, seen);

    return ans;
  }
}

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class Solution:
  def reachableNodes(
      self,
      n: int,
      edges: list[list[int]],
      restricted: list[int],
  ) -> int:
    tree = [[] for _ in range(n)]
    seen = set(restricted)

    for u, v in edges:
      tree[u].append(v)
      tree[v].append(u)

    def dfs(u: int) -> int:
      if u in seen:
        return 0
      seen.add(u)
      return 1 + sum(dfs(v) for v in tree[u])

    return dfs(0)