236. Lowest Common Ancestor of a

# 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
        """
        #either our function reached a leaf node, or encountered one of the node, carry it back out in either left or right variable, and wait for the other node to be found. 
        if root in (None, p, q): return root
        left, right = (self.lowestCommonAncestor(kid, p, q)
                   for kid in (root.left, root.right))
        #recursively look for each node in the subtrees, once we found both nodes, return the immediate root. otherwise, return the node found, and recursive back until we find the other node. 
        return root if （left and right） else （left or right）