leetcode222. 完全二叉树的节点个数

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def countNodes(self, root):
        if root is None:
            return 0
        return self.countNodes(root.left) +self.countNodes(root.right) + 1