fibonacci.rb

# OLD SOLUTION
# def fibonacci_iterative(n)
#   if n <= 1
#     return n
#   else
#     arr = [0, 1]
#     index = 0
#     (n - 1).times do
#       # arr might get very big if n is a big number
#       arr << arr[index] + arr[index + 1]
#       index += 1
#     end
#     return arr[-1]
#   end
# end

def fibonacci_iterative(n)
  if n <= 1
    return n
  else
    a, b = 0, 1
    (n - 1).times do
      # b = a + b
      # a = b - a
      a, b = b, a + b
    end
    return b
  end
end

def fibonacci_recursive(n)
  if n <= 1
    return n
  else
    fibonacci_recursive(n - 2) + fibonacci_recursive(n - 1)
  end
end

puts fibonacci_iterative(0) == 0
puts fibonacci_iterative(1) == 1
puts fibonacci_iterative(2) == 1
puts fibonacci_iterative(3) == 2
puts fibonacci_iterative(4) == 3
puts fibonacci_iterative(5) == 5
puts fibonacci_iterative(6) == 8

# puts fibonacci_recursive(0) == 0
# puts fibonacci_recursive(1) == 1
# puts fibonacci_recursive(2) == 1
# puts fibonacci_recursive(3) == 2
# puts fibonacci_recursive(4) == 3
# puts fibonacci_recursive(5) == 5
# puts fibonacci_recursive(6) == 8