题目：
示例 1：
示例 2：
代码：
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def numColor(self, root: TreeNode) -> int:
res = set()
def search(root):
if not root:
return
res.add(root.val)
search(root.left)
search(root.right)
search(root)
return len(res)
