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1443. Minimum Time to Collect All Apples in a Tree 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  int minTime(int n, vector<vector<int>>& edges, vector<bool>& hasApple) {
    vector<vector<int>> graph(n);

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

    return dfs(graph, 0, vector<bool>(n), hasApple);
  }

 private:
  int dfs(const vector<vector<int>>& graph, int u, vector<bool>&& seen,
          const vector<bool>& hasApple) {
    seen[u] = true;
    int totalCost = 0;

    for (const int v : graph[u]) {
      if (seen[v])
        continue;
      const int cost = dfs(graph, v, std::move(seen), hasApple);
      if (cost > 0 || hasApple[v])
        totalCost += cost + 2;
    }

    return totalCost;
  }
};

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class Solution {
  public int minTime(int n, int[][] edges, List<Boolean> hasApple) {
    List<Integer>[] graph = new List[n];

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

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

    return dfs(graph, 0, new boolean[n], hasApple);
  }

  private int dfs(List<Integer>[] graph, int u, boolean[] seen, List<Boolean> hasApple) {
    seen[u] = true;
    int totalCost = 0;

    for (final int v : graph[u]) {
      if (seen[v])
        continue;
      final int cost = dfs(graph, v, seen, hasApple);
      if (cost > 0 || hasApple.get(v))
        totalCost += cost + 2;
    }

    return totalCost;
  }
}