完全二叉树的节点个数222

class :
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    
    def helper(self, root, res):
        if root:
            res.append(1)
            if root.left:
                self.helper(root.left, res)
            if root.right:
                self.helper(root.right, res)

    def countNodes(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        res = []
        self.helper(root, res)
        return len(res)

# 例子
tree = TreeNode(3)
left_tree = TreeNode(9)
right_tree = TreeNode(20)
right_tree.left = TreeNode(15)
right_tree.right = TreeNode(7)
tree.left = left_tree
tree.right = right_tree
print(Solution().countNodes(tree))