Advent of Code 2023 Day 3

Day 3 seemed to confirm this would be a tough year. The puzzle gives a grid with numbers and punctuation characters like this:

467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..

Part 1 asks you to sum the numbers adjacent to one or more non-"." characters. Parsing was nontrivial. I eventually decided to create two dicts, one mapping coordinates to symbols and one mapping each coordinate with a digit to the number’s value. I used complex numbers as Cartesian coordinates. So 1+0j maps to 467.

Part 2 adds a wrinkle: you now must find each space with "*". For each that has exactly two adjacent numbers, multiply those numbers and sum up the products.

I wrote a complicated function to do both at once:

def solve(numbers, symbols, neighbors):
    gear = "*"
    counted = set()
    part1 = part2 = 0

    for coord, symbol in symbols.items():
        gear_neighbors = set()
        for neighbor in neighbors(coord):
            if neighbor in numbers:
                number = numbers[neighbor]
                if neighbor not in counted:
                    part1 += number.val
                    counted.update(number.coords)
                if symbol == gear:
                    gear_neighbors.add(frozenset(number.coords))
        if len(gear_neighbors) == 2:
            part2 += prod(numbers[next(iter(c))].val for c in gear_neighbors)

    return part1, part2

The difficulty is higher than usual, but manageable - so far.