codewars exemple

codewars.rb

#Subject
#Find the sum of the digits of all the numbers from 1 to N (both ends included).
#For N = 10 the sum is 1+2+3+4+5+6+7+8+9+(1+0) = 46
#For N = 11 the sum is 1+2+3+4+5+6+7+8+9+(1+0)+(1+1) = 48
#For N = 12 the sum is 1+2+3+4+5+6+7+8+9+(1+0)+(1+1) +(1+2)= 51
#Supported Ruby version is 1.9.3

#Tests
it 'should' do
   Test.assert_equals(solution(10), 46)
   Test.assert_equals(solution(11), 48)
   Test.assert_equals(solution(12), 51)
   Test.assert_equals(solution('12'), 51)
   Test.assert_equals(solution( 0 ), 0)
   Test.assert_equals(solution(1), 1)
end

#Basic solution
def solution(n)
  sum = 0
  (1..n.to_i).each do |c|
    c.to_s.chars.each do |i|
      sum += i.to_i
    end
  end
  sum
end

#Optimal solution
def solution(n)
  ("1".."#{n}").to_a.join.chars.map(&:to_i).inject(&:+)
end