236. Lowest Common Ancestor of a Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

Example:


Note: Not sure if the the order can be improved. Is it O(N) already?

def lowestCommonAncestor(root: 'TreeNode', p: 'TreeNode', q: 'TreeNode'):
       
    if not root:
        return None

    if root == p or root == q:
        return root

    leftLCA  = lowestCommonAncestor(root.left,  p, q)
    rightLCA = lowestCommonAncestor(root.right, p, q)

    if leftLCA and rightLCA:
        return root

    if leftLCA:
        return leftLCA;

    return rightLCA

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