1448-count-good-nodes-in-binary-tree.rb

# frozen_string_literal: true

# 1448. Count Good Nodes in Binary Tree
# https://leetcode.com/problems/count-good-nodes-in-binary-tree
# Medium

=begin
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].
=end

# Definition for a binary tree node.
# class TreeNode
#     attr_accessor :val, :left, :right
#     def initialize(val = 0, left = nil, right = nil)
#         @val = val
#         @left = left
#         @right = right
#     end
# end
# @param {TreeNode} root
# @return {Integer}
def good_nodes(root)
  @count = 0
  dfs(root, [])

  @count
end

def dfs(root, arr)
  return if root.nil?

  @count += 1 if arr.all? { |a| a <= root.val }
  arr << root.val

  dfs(root.left, arr)
  dfs(root.right, arr)

  arr.pop
end