rotate_array.rb

def rotate_array(arr, n)
  reverse(reverse(arr[0...n]) + reverse(arr[n..arr.length - 1]))
end

def reverse(arr)
  i = 0
  j = arr.length - 1

  while i < j
    temp   = arr[i]
    arr[i] = arr[j]
    arr[j] = temp
    i     += 1
    j     -= 1
  end
  arr
end