1448 Count Good Nodes in Binary Tree.py

# 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:
        """
        https://leetcode.com/problems/count-good-nodes-in-binary-tree/
        https://youtu.be/7cp5imvDzl4

        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].
        """