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814. Binary Tree Pruning 👍

  • Time: $O(n)$
  • Space: $O(h)$
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class Solution {
 public:
  TreeNode* pruneTree(TreeNode* root) {
    if (root == nullptr)
      return nullptr;
    root->left = pruneTree(root->left);
    root->right = pruneTree(root->right);
    if (root->left == nullptr && root->right == nullptr && root->val == 0)
      return nullptr;
    return root;
  }
};

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class Solution {
  public TreeNode pruneTree(TreeNode root) {
    if (root == null)
      return null;
    root.left = pruneTree(root.left);
    root.right = pruneTree(root.right);
    if (root.left == null && root.right == null && root.val == 0)
      return null;
    return root;
  }
}

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class Solution:
  def pruneTree(self, root: TreeNode | None) -> TreeNode | None:
    if not root:
      return None
    root.left = self.pruneTree(root.left)
    root.right = self.pruneTree(root.right)
    if not root.left and not root.right and not root.val:
      return None
    return root