LC1448. Count Good Nodes in Binary Tree

# 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
class Solution:
    def goodNodes(self, root: TreeNode) -> int:
        if not root: return 0
 
        def dfs(node, max_val):
            if not node:
                return 0
            
            is_good = False
 
            if node.val >= max_val:
                is_good = True
                max_val = node.val
            
            return dfs(node.left, max_val) + dfs(node.right, max_val) + int(is_good)
 
        return dfs(root, -sys.maxsize)

Complexity

Time: $O(n)$
Space: $O(log(n))$