#236. Lowest Common Ancestor of a Binary Tree
class Solution:
	def lowestCommonAncestor(self, root, p, q):
		def dfs(node):
			#if node is None or node.val == p or node.val == q:
			if node is None or node == p or node == q:
				return node 
			left = dfs(node.left)
			right = dfs(node.right)
			if left and right:
				return node 
			else:
				return left or right
		lca = dfs(root)
		return lca

"""
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
"""