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235.py
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56 lines (43 loc) · 1.49 KB
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'''
235. Lowest Common Ancestor of a Binary Search Tree
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.
'''
# 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
"""
if not root:
return None
if (p.val - root.val) * (q.val - root.val) < 0:
return root
if p.val < root.val and q.val < root.val:
return self.lowestCommonAncestor(root.left, p ,q)
elif p.val > root.val and q.val > root.val:
return self.lowestCommonAncestor(root.right, p, q)
else:
return root