236. Lowest Common Ancestor of a Binary Tree (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# 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
        """
        def dfs(node, parent):
            if node:
                node.parent = parent
                dfs(node.left, node)
                dfs(node.right, node)
        dfs(root, None)
        parents = [p]
        while p:
            parents.append(p.parent)
            p = p.parent
        while q:
            if q in parents:
                return q
            q = q.parent