main.py

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Part 1:

— Day 8: Matchsticks —

Space on the sleigh is limited this year, and so Santa will be bringing his list as a digital copy. He needs to know how much space it will take up when stored.

It is common in many programming languages to provide a way to escape special characters in strings. For example, C, JavaScript, Perl, Python, and even PHP handle special characters in very similar ways.

However, it is important to realize the difference between the number of characters in the code representation of the string literal and the number of characters in the in-memory string itself.

import re

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For example:

def test_part1() -> None:

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"" is 2 characters of code (the two double quotes), but the string contains zero characters.

    example1 = '""'
    assert len(example1) == 2
    assert character_count(example1) == 0

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"abc" is 5 characters of code, but 3 characters in the string data.

    example2 = '"abc"'
    assert len(example2) == 5
    assert character_count(example2) == 3

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"aaa\"aaa" is 10 characters of code, but the string itself contains six "a" characters and a single, escaped quote character, for a total of 7 characters in the string data.

    example3 = '"aaa\\"aaa"'
    assert len(example3) == 10
    assert character_count(example3) == 7

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"\x27" is 6 characters of code, but the string itself contains just one - an apostrophe ('), escaped using hexadecimal notation.

    example4 = '"\\x27"'
    assert len(example4) == 6
    assert character_count(example4) == 1

    example5 = '"\\\\"'
    assert len(example5) == 4
    assert character_count(example5) == 1

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Santa’s list is a file that contains many double-quoted string literals, one on each line. The only escape sequences used are \\ (which represents a single backslash), \" (which represents a lone double-quote character), and \\x plus two hexadecimal characters (which represents a single character with that ASCII code).

Disregarding the whitespace in the file, what is the number of characters of code for string literals minus the number of characters in memory for the values of the strings in total for the entire file?

For example, given the four strings above, the total number of characters of string code (2 + 5 + 10 + 6 = 23) minus the total number of characters in memory for string values (0 + 3 + 7 + 1 = 11) is 23 - 11 = 12.

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Part 1 Solution:

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Immediately I want to try using regex to count how many encoding patterns are matched in the string.

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Return the number of characters encoded in the raw string.

def character_count(raw_string: str) -> int:

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First, remove the beginning and end double quote.

    clipped_string = raw_string[1:-1]

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Then match all the encoding patterns possible and return the number of matches.

    return len(re.findall(r'\\x[0-9a-fA-F]{2}|\\"|\\\\|.', clipped_string))

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Split the input lines and then count up the total input string lengths and encoded character counts. Then return the different between the two

def part1(input: str) -> int:

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Part 2:

— Part Two —

Now, let’s go the other way. In addition to finding the number of characters of code, you should now encode each code representation as a new string and find the number of characters of the new encoded representation, including the surrounding double quotes.

    total_string_length = 0
    total_character_count = 0

    for raw_string in input.strip().splitlines():
        total_string_length += len(raw_string)
        total_character_count += character_count(raw_string)

    return total_string_length - total_character_count

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For example:

def test_part2() -> None:

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"" encodes to "\"\"", an increase from 2 characters to 6.

    example1 = '""'
    assert len(example1) == 2
    assert string_repr(example1) == '"\\"\\""'
    assert len(string_repr(example1)) == 6

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"abc" encodes to "\"abc\"", an increase from 5 characters to 9.

    example1 = '"abc"'
    assert len(example1) == 5
    assert string_repr(example1) == '"\\"abc\\""'
    assert len(string_repr(example1)) == 9

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"aaa\"aaa" encodes to "\"aaa\\\"aaa\"", an increase from 10 characters to 16.

    example1 = '"aaa\\"aaa"'
    assert len(example1) == 10
    assert string_repr(example1) == '"\\"aaa\\\\\\"aaa\\""'
    assert len(string_repr(example1)) == 16

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"\x27" encodes to "\"\\x27\"", an increase from 6 characters to 11.

    example1 = '"\\x27"'
    assert len(example1) == 6
    assert string_repr(example1) == '"\\"\\\\x27\\""'
    assert len(string_repr(example1)) == 11

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Your task is to find the total number of characters to represent the newly encoded strings minus the number of characters of code in each original string literal. For example, for the strings above, the total encoded length (6 + 9 + 16 + 11 = 42) minus the characters in the original code representation (23, just like in the first part of this puzzle) is 42 - 23 = 19.

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Part 2 Solution:

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Again, regex calls to me.

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Return the escaped representation of the given string.

def string_repr(string: str) -> str:

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Put a backslash in front of any double quote or backslash characters.

    s = re.sub(r'("|\\)', r"\\\1", string)
    return '"' + s + '"'

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Split the input lines and then count up the total input string lengths and the total number of characters in their escaped string representations. Return the difference of the two

def part2(input: str) -> int:

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    total_string_length = 0
    total_repr_length = 0

    for raw_string in input.strip().splitlines():
        total_string_length += len(raw_string)
        total_repr_length += len(string_repr(raw_string))

    return total_repr_length - total_string_length


if __name__ == "__main__":
    puzzle_input = open("input.txt").read()

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Print out part 1 solution

    print("Part 1:", part1(puzzle_input))

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Print out part 2 solution

    print("Part 2:", part2(puzzle_input))