Notebook

The set of all misplaced items¶

https://adventofcode.com/2022/day/3

We are asked to find the single common element between two compartments in a rucksack. This is what sets are really great for, the intersection of the two sets of letters.

In [1]:

import string

priorities = {letter: i for i, letter in enumerate(string.ascii_letters, 1)}


def misplaced_item(rucksack: str) -> str:
    half = len(rucksack) // 2
    [letter] = set(rucksack[:half]) & set(rucksack[half:])
    return letter


example = """\
vJrwpWtwJgWrhcsFMMfFFhFp
jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
PmmdzqPrVvPwwTWBwg
wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
ttgJtRGJQctTZtZT
CrZsJsPPZsGzwwsLwLmpwMDw
""".splitlines()


assert sum(priorities[misplaced_item(r)] for r in example) == 157

In [2]:

import aocd

rucksacks = aocd.get_data(day=3, year=2022).splitlines()
print("Part 1:", sum(priorities[misplaced_item(r)] for r in rucksacks))

Part 1: 7763

Part 2, intersecting more than 2¶

The problem hasn't really changed, we now have to intersect 3 rucksacks to find the single item. Since the set().intersection() method can take multiple inputs, this is trivial to achieve.

In [3]:

from typing import Iterator


def badge(rucksack: str, *rucksacks: str) -> str:
    [letter] = set(rucksack).intersection(*rucksacks)
    return letter


def badges(*rucksacks: str) -> Iterator[str]:
    it = iter(rucksacks)
    for group in zip(it, it, it):
        yield badge(*group)


assert sum(priorities[badge] for badge in badges(*example)) == 70

In [4]:

print("Part 2:", sum(priorities[badge] for badge in badges(*rucksacks)))

Part 2: 2569