Count Good Nodes in Binary Tree

• https://leetcode.com/problems/count-good-nodes-in-binary-tree/
• Preorder traversal while keeping track of maximum

# 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:
        
        def dfs(node, curr_max):
            if node == None:
                return 0
            
            res = 1 if (node.val >= curr_max) else 0
            curr_max = max(curr_max, node.val)
            res += dfs(node.left, curr_max)
            res += dfs(node.right, curr_max)
            
            return res
            
        return dfs(root, root.val)