# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right

#Just check the whether the left and right subtrue are uni-value or not
#If left and right subtruee are uni-vale, then check whether the node value and the value of two subtrees are the same

class Solution:
    def countUnivalSubtrees(self, root: TreeNode) -> int:
        self.res = 0
        self.dfs(root)

        return self.res

    def dfs(self, root):

        if not root:
            return [True, None]

        left, left_val = self.dfs(root.left)
        right, right_val = self.dfs(root.right)

        Bool = False

        if left and right:
            if left_val is None and right_val is None:
                Bool = True
            elif left_val is None:
                Bool = (root.val == right_val)
            elif right_val is None:
                Bool = (root.val == left_val)
            else:
                Bool = (root.val == left_val) and (root.val == right_val)
        if Bool:
            self.res += 1
        return [Bool, root.val]