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[7/26] 236. Lowest Common Ancestor of a Binary Tree

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236. Lowest Common Ancestor of a Binary Tree

Medium

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Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.

According to the definition 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 allow a node to be a descendant of itself).”

Example 1:

Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
Output: 3
Explanation: The LCA of nodes 5 and 1 is 3.

Example 2:

Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
Output: 5
Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

Example 3:

Input: root = [1,2], p = 1, q = 2
Output: 1

Constraints:

The number of nodes in the tree is in the range [2, 105].
-109 <= Node.val <= 109
All Node.val are unique.
p != q
p and q will exist in the tree.

Accepted

1,073,775

Submissions

1,901,179

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링크

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/ 2151 회 연결

익명
작성일 2022.07.25 21:10

Runtime: 115 ms, faster than 45.34% of Python3 online submissions for Lowest Common Ancestor of a Binary Tree.
Memory Usage: 26.4 MB, less than 17.99% of Python3 online submissions for Lowest Common Ancestor of a Binary Tree.

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if not root: return None
        if root == p or root==q: return root
        
        
        left = self.lowestCommonAncestor(root.left, p, q)
        right = self.lowestCommonAncestor(root.right, p, q)
        
        if left and right: return root
        
        return left or right