Question

Hello everyone. This questions pertains to problem set 4, question number 4a. We are supposed to write a multi-level decryption algorithm that calls itself recursively and returns a group of tuples that can be used to decode the ciphertext. I am a bit stumped at the moment with the start variable. What does it do, also, what is the correct base case?

Answer 1

Hi! I just got done with problem set 4. It's a really tough one!! start is used to mark the place where the encrypted text starts. If you've already done problem 3 start is just the first variable in each of the tuples. but inside find_best_shifts_rec, it's really useful for recursion.

As for the base case, this is my design

RECURSIVE DESIGN:

BASE CASES:
if all the words in the decoded text are valid
return a list with a tuple of the position and shift

if there are no valid words in the decoded text
return none

RECURSIVE CASE:
if the recursion doesn't return none
return a list with a tuple of the start position and shift joined
with the recursion