LeetCode LCR 44 - 开幕式焰火

class Solution:
    def numColor(self, root: TreeNode) -> int:
        # 哈希表记录颜色
        hash = set()
        def numColorIMPL(root):
            nonlocal hash
            if not root:
                return
            if root.val not in hash:
                hash.add(root.val)
            numColorIMPL(root.left)
            numColorIMPL(root.right)
        numColorIMPL(root)
        return len(hash)