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1448. Count Good Nodes in Binary Tree 👍

  • Time: $O(n)$
  • Space: $O(h)$
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class Solution {
 public:
  int goodNodes(TreeNode* root, int mx = INT_MIN) {
    if (root == nullptr)
      return 0;
    const int newMax = max(mx, root->val);
    return (root->val >= mx) +              //
           goodNodes(root->left, newMax) +  //
           goodNodes(root->right, newMax);
  }
};

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class Solution {
  public int goodNodes(TreeNode root) {
    return goodNodes(root, Integer.MIN_VALUE);
  }

  private int goodNodes(TreeNode root, int mx) {
    if (root == null)
      return 0;

    final int newMax = Math.max(mx, root.val);
    return (root.val >= mx ? 1 : 0) + goodNodes(root.left, newMax) + goodNodes(root.right, newMax);
  }
}