Advent of Code 2023

https://adventofcode.com/2023

Insights & Learnings

Day 2

Bitwise operators with Counters

Counters can be combined with a key-wise max using | .

from collections import Counter

a = Counter({ "a": 1, "b": 2, "c": 4})
b = Counter({ "b": 9, "c": 3, "d": 1})

print(a | b)
print(a & b)

Counter({'b': 9, 'c': 4, 'a': 1, 'd': 1})
Counter({'c': 3, 'b': 2})

The and operation only gives the intersecting keys. Which may not be desired, I couldn't find a way to do this without creating other data structures.

These operations can also be done in place with |= and &=

You can use these operations in functools.reduce by passing operator.or_ or Counter.__or__ as the first argument.

e.g. What characters do we need so that we can display any one of these film titles on our Cinema hording?

from collections import Counter
from functools import reduce
from operator import or_

FILMS = [
    "Back to the future",
    "A View to a Kill",
    "Beverly Hills Cop",
    "Witness",
    "Amadeus",
    "The Terminator",
    "Cocoon",
    "Legend",
    "A Nightmare on Elm Street",
    "The Goonies"
]

print(
    "".join(
        sorted(
            reduce(
                or_,
                ( Counter(film) for film in FILMS )
            ).elements()
        )
    ).strip()
)

ABCEGHKLNSTTVWacdeeefghiiklllmmnoooprrsstttuuvwy

In Python 3.12 the only difference between using operator.or_ or Counter.__or__ was that or_ is loaded directly wheras __or__ requires loading Counter and then loading the __or__ attribute. A function passed to reduce is loaded only once, this will be the same for any itertools or functools function that accept another function, so use either.

No need to do any grouping by each handful of dice

When testing to see if there were too many dice or getting the most dice seen for a colour we didn't need to group by handful.

It would have been nice to split strings on multiple substrings ", " and "; . The simplest workaround was to pre-process the string with a replace so they were all the same.

No need to parse and keep the Game number

This was a nice pattern to sum the game numbers that were legitimate:

sum(mul(*pair) for pair in enumerate(<bool_sequence>, 1))