The Weekly Challenge 287, Task 1

You are given a string, $str.
Write a program to return the minimum number of steps required to make the given string very strong password. If it is already strong then return 0.
Criteria:

• It must have at least 6 characters.
• It must contains at least one lowercase letter, at least one upper case letter and at least one digit.
• It shouldn’t contain 3 repeating characters in a row.

Following can be considered as one step:

• Insert one character;
• Delete one character;
• Replace one character with another.

A Simplification

To make the algorithm simpler, let’s ignore deletion. Instead of deleting a character, we can always replace it with a character different to the original one and its neighbours (you can easily verify that it can’t break any of the three criteria: it doesn’t shorten the password, it doesn’t remove more characters than the deletion would have deleted, and it never creates repeating characters).

The Algorithm

Let’s keep a set of strings we need to check, we’ll call them the agenda. At the start of the program, the agenda contains the input string.