input: Write a python function to calculate the Fibonacci sequence both with and without memoization.
  assert fibonacci(5) == 5
  assert fibonacci(10) == 55
  assert fibonacci_memoize(5, [None] * 6) == 5
  assert fibonacci_memoize(10, [None] * 11) == 55
output: def fibonacci(n):
      if n <= 1:
          return n
      return fibonacci(n - 1) + fibonacci(n - 2)
  
  def fibonacci_memoize(n, memo):
      if memo[n] is not None:
          return memo[n]
      if n <= 1:
          memo[n] = n
      else:
          memo[n] = fibonacci_memoize(n - 1, memo) + fibonacci_memoize(n - 2, memo)
      return memo[n]