binary_tree_paths.rb

# 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 {String[]}

def construct_paths(root, path, paths)
    if root
        path += root.val.to_s
    
        if root.left.nil? && root.right.nil?
            paths << path
        else
            path += '->'
            construct_paths(root.left, path, paths)
            construct_paths(root.right, path, paths)
        end
    end 
end

def binary_tree_paths(root)
    paths = []
    construct_paths(root, '', paths)
    return paths
end