reverse_number.rb

# An algorithm to reverse a number using only mathematical functions, i.e. no
# String.reverse, or similar. For example, turn `1234` into `4321`.

def reverse_number(number)
  digit_count = Math.log10(number).floor + 1
  sum = 0
  (1..digit_count).each do |power|
    ten_to_the_n = 10.0**power
    ten_to_the_n_minus_one = 10.0**(power - 1)
    remainder = number % ten_to_the_n
    digit = (remainder / ten_to_the_n_minus_one).floor
    magnitude = digit_count - power
    sum += digit * 10**magnitude
  end
  sum
end