How to write this iterative function to be recursive?

Question

I need to write this iterative function to do the same thing but it must be recursive.

def task1(string: str):
    for i in range(len(string)):
        if string[i] != string[len(string) - i - 1]:
            return False
    return True

This is what i tried but it does not work.

def task1_recursion(string: str):
    print(string)
    if len(string) > 1:
        if string[0] == task1_recursion(string[1::1]):
            return True
        else:
            return False
    else:
        return string

My code seems to one the last recursion return string "" and that makes it to return False.

Answer 1

Just check the tip and the tail, continue with the string without them:

def task1_recursion(string: str):
    # recursion base condition (exit condition)
    if len(string) <= 1:
        return True
    # unpack values
    first, *_, last = string
    # check if they are different
    if first != last:
        return False
    # if not continue checking the remaining string
    return task1_recursion(string[1:-1])

Answer 2

If I understand correctly you want to check if a string is symmetric with the code in task1 . My solution is below:

def fct(s: str, i: int):
    if len(s) <= 1 or i == len(s):
        return True
    return s[i] == s[len(s) - 1 - i] and fct(s, i + 1)

I tested and fct produces the same result as task1 . It needs an additional parameter for the index though. But you can wrap it inside another function if you want the parameter to include only the input string. i is always set to 0 when you call the function, eg fct("ABCCBA", 0) .