leetcode222

 1 class Solution:
 2     def __init__(self):
 3         self.count = 0
 4         
 5     def preOrder(self,node):
 6         if node != None:
 7             self.count += 1
 8             self.preOrder(node.left)
 9             self.preOrder(node.right)
10         
11     def countNodes(self, root: TreeNode) -> int:
12         self.preOrder(root)
13         return self.count