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.
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# Return the number of good nodes in the binary tree.
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# Example 1:
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# 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.
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# Example 2:
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# Input: root = [3,3,null,4,2]
# Output: 3
# Explanation: Node 2 -> (3, 3, 2) is not good, because "3" is higher than it.
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# Example 3:
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# Input: root = [1]
# Output: 1
# Explanation: Root is considered as good.
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# Constraints:
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# 	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].
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# 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:
        count = 0
        stack = [(root, root.val)]
        while len(stack) > 0:
            current, val = stack.pop()
            if current.val >= val: count += 1
            if current.right: 
                stack.append((current.right, max(current.val, val)))
            if current.left: 
                stack.append((current.left, max(current.val, val)))
        return count