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235_Lowest_Common_Ancestor_of_a_Binary_Search_Tree.py
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235_Lowest_Common_Ancestor_of_a_Binary_Search_Tree.py
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# Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
#
# According to the definition of LCA on Wikipedia:
# "The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as
# descendants (where we allow a node to be a descendant of itself)."
#
# _______6______
# / \
# ___2__ ___8__
# / \ / \
# 0 _4 7 9
# / \
# 3 5
#
# For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6.
# Another example is LCA of nodes 2 and 4 is 2,
# since a node can be a descendant of itself according to the LCA definition.
#
# Tags: Tree
# Difficulty: Easy
# Definition for a binary tree node.
class TreeNode(object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution(object):
def lowestCommonAncestor(self, root, p, q):
"""
:type root: TreeNode
:type p: TreeNode
:type q: TreeNode
:rtype: TreeNode
"""
small, big = (p.val, q.val) if p.val < q.val else (q.val, p.val)
while not small <= root.val <= big:
root = root.left if big < root.val else root.right
return root