Lowest Common Ancestor of a Binary Search Tree(递归)
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
According to thedefinition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allowa node to be a descendant of itself).”
Given binary search tree: root = [6,2,8,0,4,7,9,null,null,3,5]
_______6______
/ \
___2__ ___8__
/ \ / \
0 _4 7 9
/ \
3 5
Example 1:
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
Explanation: The LCA of nodes 2 and 8 is 6.
Example 2:
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself
according to the LCA definition.
Note:
All of the nodes' values will be unique.
p and q are different and both values will exist in the BST.
分析:
分治
# 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, p, q):
"""
:type root: TreeNode
:type p: TreeNode
:type q: TreeNode
:rtype: TreeNode
"""
if root in (None,p,q):
return root
if (root.val - p.val) * (root.val - q.val)<1:
return root
elif root.val < p.val:
return self.lowestCommonAncestor(root.right,q,p)
else:
return self.lowestCommonAncestor(root.left, q, p)
Last updated
Was this helpful?