Day 5: Doesn’t He Have Intern-Elves For This?

Part 1

Santa needs help figuring out which strings in his text file are naughty or nice.

A nice string is one with all of the following properties:

• It contains at least three vowels (aeiou only), like aei, xazegov, or aeiouaeiouaeiou.
• It contains at least one letter that appears twice in a row, like xx, abcdde (dd), or aabbccdd (aa, bb, cc, or dd).
• It does not contain the strings ab, cd, pq, or xy, even if they are part of one of the other requirements.

For example:

• ugknbfddgicrmopn is nice because it has at least three vowels (u...i...o...), a double letter (...dd...), and none of the disallowed substrings.
• aaa is nice because it has at least three vowels and a double letter, even though the letters used by different rules overlap.
• jchzalrnumimnmhp is naughty because it has no double letter.
• haegwjzuvuyypxyu is naughty because it contains the string xy.
• dvszwmarrgswjxmb is naughty because it contains only one vowel.

0. Load Puzzle input

file = open('puzzle.aoc', 'r')

1. Define rules

def more_than_two_vowels(input):
    """Check if more than two vowels are in string"""
    vowels = input.count('a') + input.count('e') + input.count('i') + input.count('o') + input.count('u')
    return vowels > 2

def two_letters_in_a_row(input):
    """Check if one letter follows itself at least once"""
    prev = ''
    for current in input:
        if prev == current:
            return True
        prev = current
    return False

def does_not_contain_forbidden_seqs(input):
    """Does not contain 'ab', 'cd', 'pq' or 'xy'"""
    appearances = input.count('ab') + input.count('cd') + input.count('pq') + input.count('xy')
    return appearances == 0

Task 1: How many strings are nice?

2. Count nice strings

nice_strings = 0

while True:
    line = file.readline()
 
    if more_than_two_vowels(line) and \
        two_letters_in_a_row(line) and \
        does_not_contain_forbidden_seqs(line):
        nice_strings += 1
        
    # if end of file is reached
    if not line:
        break

3. Show nice Strings

nice_strings

4. Close file

file.close()

Part 2

0. Load puzzle input

file = open('puzzle.aoc', 'r')

Realizing the error of his ways, Santa has switched to a better model of determining whether a string is naughty or nice. None of the old rules apply, as they are all clearly ridiculous.

Now, a nice string is one with all of the following properties:

• It contains a pair of any two letters that appears at least twice in the string without overlapping, like xyxy (xy) or aabcdefgaa (aa), but not like aaa (aa, but it overlaps).
• It contains at least one letter which repeats with exactly one letter between them, like xyx, abcdefeghi (efe), or even aaa.

For example:

• qjhvhtzxzqqjkmpb is nice because is has a pair that appears twice (qj) and a letter that repeats with exactly one letter between them (zxz).
• xxyxx is nice because it has a pair that appears twice and a letter that repeats with one between, even though the letters used by each rule overlap.
• uurcxstgmygtbstg is naughty because it has a pair (tg) but no repeat with a single letter between them.
• ieodomkazucvgmuy is naughty because it has a repeating letter with one between (odo), but no pair that appears twice.

1. Define new rules

def pair_appears_twice(input):
    """Contains two appearances of pairs"""
    for i in range(len(input)):
        if input[i+2:].count(input[i:i+2]) > 0:
            return True
    return False

def pair_is_seperated(input):
    """Check if a pair is seperated through another character"""
    preprev = '\0'
    prev = ''
    for current in input:
        if preprev == current:
            return True
        preprev = prev
        prev = current
    return False

Task 2: How many strings are nice under these new rules?

2. Count nice strings

nice_strings = 0

while True:
    line = file.readline()
 
    if pair_appears_twice(line) and \
        pair_is_seperated(line):
        nice_strings += 1
        
    # if end of file is reached
    if not line:
        break

3. Show amount of nice strings

nice_strings

4. Close file

file.close()