235. Lowest Common Ancestor of a Binary Search Tree
2015-12-23 11:35
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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).”
For example, the lowest common ancestor (LCA) of nodes
Another example is LCA of nodes
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
"""
a=root
if q.val>p.val:
t=p
p=q
q=t
if root==None:
return root
while q.val>a.val or a.val>p.val:
if q.val>a.val:
a=a.right
if a.val>p.val:
a=a.left
if a==None:
break
return a
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
2and
8is
6.
Another example is LCA of nodes
2and
4is
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
"""
a=root
if q.val>p.val:
t=p
p=q
q=t
if root==None:
return root
while q.val>a.val or a.val>p.val:
if q.val>a.val:
a=a.right
if a.val>p.val:
a=a.left
if a==None:
break
return a
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