Climb the stairs (brain friendly, not so cpu friendly)

README

There's a staircase with N steps, and you can climb 1 or 2 steps at a time. 
Given N, write a function that returns the number of unique ways you can 
climb the staircase. The order of the steps matters.
 
For example, if N is 4, then there are 5 unique ways:
 
 1, 1, 1, 1
 2, 1, 1
 1, 2, 1
 1, 1, 2 
 2, 2
 
What if, instead of being able to climb 1 or 2 steps at a time, you could 
climb any number from a set of positive integers X? 

For example, if X = {1, 3, 5}, you could climb 1, 3, or 5 steps at a time.
Generalize your function to take in X.

steps.rb

def steps(x, n)
  raw_tree = x.map { |i| [i] }
  final_tree = []

  loop do
    raw_tree, final_leaves = raw_tree
      .each_with_object([]) { |leaf, tree| x.each { |i| tree << leaf.dup.push(i) } }
      .delete_if { |leaf| leaf.inject(:+) > n } 
      .partition { |leaf| leaf.inject(:+) < n } 

    final_tree.concat final_leaves

    break if raw_tree.empty?
  end

  final_tree
end

puts steps([1,2],4).to_s
puts steps([1,3,5],10).to_s