235-lowest-common-ancestor-of-a-binary-search-tree.py

# 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':
        cur = root
        while cur:
            if cur.val > p.val and cur.val > q.val:
                cur = cur.left
            elif cur.val < p.val and cur.val < q.val:
                cur = cur.right
            else:
                break
        return cur
    
# time O(n), due to tree height
# space O(1)
# using tree and divide and conquer and find LCA and bst