This is the last month of my goal toward 150 problems done by 2025. I’ll have to pick up more than a few problems this weekend. I have 56 problems remaining.

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Solution

from collections import deque

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if root in (None, p, q): return root
        left, right = [self.lowestCommonAncestor(kid, p, q) for kid in (root.left, root.right)]
        return root if left and right else left or right
            

Time complexity is O(n) = n and space complexity is O(h) where the height is h. Best case the height is log(n) as a balanced tree and worst case is n as a skewed tree.