Challenges from https://medium.com/better-programming/practicing-recursion-with-7-algorithm-challenges-7ffdd634557

recursive.py

from functools import lru_cache

def flip(text):
    if not text:
        return ''
    return text[-1] + flip(text[:-1])

def addingUpTo(numbers, idx):
    try:
        if idx >= 0:
            return numbers[idx] + addingUpTo(numbers, idx-1)
        else:
            return 0
    except IndexError:
        return addingUpTo(numbers, idx-1)

def maxOf(numbers):
    if numbers:
        submax = maxOf(numbers[:-1])
        if submax is None:
            return numbers[-1]
        return max(numbers[-1], submax)
    else:
        return None

def includesNumber(numbers, num):
    if numbers:
        if numbers[-1] == num:
            return True
        else:
            return includesNumber(numbers[:-1], num)
    else:
        return False

def isPalindrome(text):
    if text:
        return text[0] == text[-1] and isPalindrome(text[1:-1])
    else:
        return True

@lru_cache
def permutations(text):
    if len(text) >= 2:
        p = []
        for idx, letter in enumerate(text):
            subtext = text[0:idx] + text[idx+1:]
            subps = permutations(subtext)
            for subp in subps:
                if not (letter + subp) in p:
                    p.append(letter + subp)
        return p
    else:
        return [text]

@lru_cache
def fib(n):
    if n == 0 or n == 1:
        return n
    return fib(n-1) + fib(n-2)