［LeetCode］236. Lowest Common Ancestor of a Binary Tree

236. Lowest Common Ancestor of a Binary Tree

# 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 lca(node):
            if not node:
                return None
            # 找到p或者q
            if node == p or node == q:
                return node
            left = lca(node.left)
            right = lca(node.right)
            # 如果同时存在，表明当前结点则为lca，其余均为处在同个方向上。
            if left and right:
                return node
            elif left:
                return left
            elif right:
                return right
            else:
                return None
        return lca(root)