0129-sum-root-to-leaf-numbers.rb

# frozen_string_literal: true

# 129. Sum Root to Leaf Numbers
# https://leetcode.com/problems/sum-root-to-leaf-numbers

=begin

You are given the root of a binary tree containing digits from 0 to 9 only.

Each root-to-leaf path in the tree represents a number.

* For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.
Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer.

A leaf node is a node with no children.

### Constraints:

* The number of nodes in the tree is in the range [1, 1000].
* 0 <= Node.val <= 9
* The depth of the tree will not exceed 10.

=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 sum_numbers(root, n = 0)
  n, l, r = n * 10 + root.val, root.left, root.right
  !l && !r ? n :
    (l ? sum_numbers(l, n) : 0) +
    (r ? sum_numbers(r, n) : 0)
end