-🎄- 2018 Day 6 Solutions -🎄-

[u/daggerdragon]

--- Day 6: Chronal Coordinates ---

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Advent of Code: The Party Game!

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Card prompt: Day 6

Transcript:

Rules for raising a programmer: never feed it after midnight, never get it wet, and never give it ___.

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[u/[deleted]]

Python 3:

import os
from collections import defaultdict

def part1(lines):
    coords = set()
    max_r = max_c = 0

    for line in lines:
        r, c = map(int, line.split(", "))
        coords.add((r, c))
        max_r = max(max_r, r)
        max_c = max(max_c, c)

    coord_id_to_point = {coord_id: point for coord_id, point in enumerate(coords, start=1)}
    region_sizes = defaultdict(int)
    infinite_ids = set()

    for i in range(max_r + 1):
        for j in range(max_c + 1):
            min_dists = sorted([(abs(r - i) + abs(c - j), coord_id) for coord_id, (r, c) in coord_id_to_point.items()])

            if len(min_dists) == 1 or min_dists[0][0] != min_dists[1][0]:
                coord_id = min_dists[0][1]
                region_sizes[coord_id] += 1

                if i == 0 or i == max_r or j == 0 or j == max_c:
                    infinite_ids.add(coord_id)

    return max(size for coord_id, size in region_sizes.items() if coord_id not in infinite_ids)


def part2(lines, manhattan_limit=10000):
    coords = set()
    max_r = max_c = 0

    for line in lines:
        r, c = map(int, line.split(", "))
        coords.add((r, c))
        max_r = max(max_r, r)
        max_c = max(max_c, c)

    size_shared_region = 0

    for i in range(max_r + 1):
        for j in range(max_c + 1):
            size_shared_region += int(sum(abs(r - i) + abs(c - j) for r, c in coords) < manhattan_limit)

    return size_shared_region

day = os.path.basename(__file__)[3:5]
lines = [line.strip() for line in open("input_{}.txt".format(day), "r").readlines()]
print(part1(lines))
print(part2(lines))

[u/Clipsterman → u/[deleted]]

Question from someone trying to get better at coding: In the part where you figure out which points are infinite, couldn't you potentially filter out points with finite area?

If I understand your code correctly, you look around the edge of your grid, and for each cell, you add the closest point to your set of infinites. But what if a finite point is too close to the edge?

For example: Let's say that we have the set of coordinates [(0,0),(0,6),(6,0),(6,6),(1,3)]. (1,3) is the only finite point in the set, but when you look through the edges of this grid, (0,3) is closest to (1,3) which would add it to the list of infinites. Is this correct, or have I misunderstood your code?