sum of digits

sum_of_digits.rb

### solution 1
def sum_of_digits n
  n.to_s.split('').inject(0) {|sum, i| sum + i.to_i}
end

### solution 2
def sum_of_digits n
  sum = 0
  while n > 0 do
    d = n / 10
    r = n % 10
    sum += r
    n -= r
    n /= 10 if d > 0
  end
  sum
end