0112-path-sum.rb

# frozen_string_literal: true

# 112. Path Sum
# https://leetcode.com/problems/path-sum
# Easy

=begin
Given the root of a binary tree and an integer targetSum, return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum.

A leaf is a node with no children.

Example 1:
Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
Output: true
Explanation: The root-to-leaf path with the target sum is shown.

Example 2:
Input: root = [1,2,3], targetSum = 5
Output: false
Explanation: There two root-to-leaf paths in the tree:
(1 --> 2): The sum is 3.
(1 --> 3): The sum is 4.
There is no root-to-leaf path with sum = 5.

Example 3:
Input: root = [], targetSum = 0
Output: false
Explanation: Since the tree is empty, there are no root-to-leaf paths.

Constraints:
* The number of nodes in the tree is in the range [0, 5000].
* -1000 <= Node.val <= 1000
* -1000 <= targetSum <= 1000
=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
# @param {Integer} target_sum
# @return {Boolean}
def has_path_sum(root, target_sum)
  return false if root.nil?

  if root.val == target_sum && root.left.nil? && root.right.nil?
    return true
  end

  has_path_sum(root.left, target_sum - root.val) || has_path_sum(root.right, target_sum - root.val)
end