aoc2024day8.py

# === Parsing ===

antennas = {}
with open("input.txt", "r") as f:
    for y, line in enumerate(f):
        for x, char in enumerate(line.strip()):
            if char != ".":
                antennas.setdefault(char, set()).add((x, y))

    max_x = x
    max_y = y

print(antennas)


# === Part 1 ===
from itertools import combinations


antinodes = set()
for antenna_group in antennas.values():
    for (x1, y1), (x2, y2) in combinations(antenna_group, 2):
        dx, dy = x1 - x2, y1 - y2
        ax, ay = x1 + dx, y1 + dy
        if 0 <= ax <= max_x and 0 <= ay <= max_y:
            antinodes.add((ax, ay))
        ax, ay = x2 - dx, y2 - dy
        if 0 <= ax <= max_x and 0 <= ay <= max_y:
            antinodes.add((ax, ay))

print(len(antinodes))


# === Part 2 ===
from itertools import combinations


antinodes = set()
for antenna_group in antennas.values():
    for (x1, y1), (x2, y2) in combinations(antenna_group, 2):
        dx, dy = x1 - x2, y1 - y2
        step = 0
        while 0 <= x1 + step * dx <= max_x and 0 <= y1 + step * dy <= max_y:
            antinodes.add((x1 + step * dx, y1 + step * dy))
            step += 1
        step = 0
        while 0 <= x1 - step * dx <= max_x and 0 <= y1 - step * dy <= max_y:
            antinodes.add((x1 - step * dx, y1 - step * dy))
            step += 1

print(len(antinodes))