12_integer_to_roman.rb

# @param {Integer} num
# @return {String}
def int_to_roman(num)
  rst = ""
  romans = {1 => 'I', 5 => 'V', 10 => 'X', 50 => 'L', 100 => 'C', 500 => 'D', 1000 => 'M'}
  num.digits.each_with_index do |n, idx|
    next if n == 0
    char = 
      if n < 4
        romans[10 ** idx] * n
      elsif n == 4
        romans[10 ** idx] + romans[10 ** idx * 5]
      elsif n == 9
        romans[10 ** idx] + romans[10 ** idx * 10]
      else
        romans[10 ** idx * 5] + romans[10 ** idx] * (n % 5)
      end
    rst.prepend char
  end
  rst
end

#简化
def int_to_roman(num)
  rst = ""
  romans = %w(I V X L C D M)
  num.digits.each_with_index do |n, idx|
    next if n == 0
    char = 
      if n < 4
        romans[idx * 2] * n
      elsif n == 4
        romans[idx * 2] + romans[idx * 2 + 1]
      elsif n == 9
        romans[idx * 2] + romans[idx * 2 + 2]
      else
        romans[idx * 2 + 1] + romans[idx * 2] * (n % 5)
      end
    rst.prepend char
  end
  rst
end