Binary strings

# title: Binary strings
# source: https://rosettacode.org/wiki/Binary_strings
# category: Rosetta Code
# difficulty: Intro
# summary: Generate all binary strings of a fixed length with a simple recursive builder.
# tags: popular, strings, recursion, combinatorics
# vibe: 0.2

def binary_strings(length)
  if length == 0
    [""]
  else
    tails = binary_strings(length - 1)
    output = []
    index = 0
    while index < tails.length
      output = output.push("0" + tails[index])
      output = output.push("1" + tails[index])
      index = index + 1
    end
    output
  end
end

def run
  {
    length_three: binary_strings(3),
    length_four_count: binary_strings(4).length
  }
end