1448. Count Good Nodes in Binary Tree.py

'''
Given a binary tree root, a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X.

Return the number of good nodes in the binary tree.

 

Example 1:



Input: root = [3,1,4,3,null,1,5]
Output: 4
Explanation: Nodes in blue are good.
Root Node (3) is always a good node.
Node 4 -> (3,4) is the maximum value in the path starting from the root.
Node 5 -> (3,4,5) is the maximum value in the path
Node 3 -> (3,1,3) is the maximum value in the path.
Example 2:



Input: root = [3,3,null,4,2]
Output: 3
Explanation: Node 2 -> (3, 3, 2) is not good, because "3" is higher than it.
Example 3:

Input: root = [1]
Output: 1
Explanation: Root is considered as good.
 

Constraints:

The number of nodes in the binary tree is in the range [1, 10^5].
Each node's value is between [-10^4, 10^4].
'''

# 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


mx = 0
class Solution:
    def goodNodes(self, root: TreeNode) -> int:
        global mx
        mx = 0
        if root==None:
            return 0
        
        maxVal = root.val
        dfs(root, maxVal)
        return mx


def dfs(root, maxVal):
    global mx
    if root==None:
        return
    
    if root.val>=maxVal:
        mx+=1
        
    dfs(root.left, max(maxVal, root.val))
    dfs(root.right, max(maxVal, root.val))