Integer to Roman. Assumes n >= 0

int_to_roman.rb

ROMANS = {
  1 => "I",
  4 => "IV",
  5 => "V",
  10 => "X",
  40 => "XL",
  50 => "L",
  90 => "XC",
  100 => "C",
  400 => "CD",
  500 => "D",
  900 => "CM",
  1000 => "M",
}

def solution(n)
  if n == 0
    return ""
  end
  
  current_int = closest_less_or_equal(n, ROMANS.keys)
  ROMANS[current_int] + solution(n - current_int)
end

def closest_less_or_equal(n, ints)
  ints.select { |int| int <= n }.max
end