From 11cf6db02ace54d2b46ecb86711b3043a42f99f9 Mon Sep 17 00:00:00 2001
From: Drew Winstel <drew@hsv.beer>
Date: Thu, 24 Dec 2020 06:56:25 -0600
Subject: [PATCH] Add Drew's day 24 solution

It's slow (about 72 sec) but it works.
---
 Drew/drew_day24.py | 181 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 181 insertions(+)
 create mode 100644 Drew/drew_day24.py

diff --git a/Drew/drew_day24.py b/Drew/drew_day24.py
new file mode 100644
index 0000000..5c2fa77
--- /dev/null
+++ b/Drew/drew_day24.py
@@ -0,0 +1,181 @@
+"""Day 24: Lobby layout
+
+Coordinate system taken from
+https://www.redblobgames.com/grids/hexagons/#coordinates
+"""
+
+from collections import defaultdict
+from day23 import REAL_INPUT
+from typing import Dict, List, Tuple
+
+
+MOVES = {
+    "e": [1, -1, 0],
+    "w": [-1, 1, 0],
+    "se": [0, -1, 1],
+    "sw": [-1, 0, 1],
+    "nw": [0, 1, -1],
+    "ne": [1, 0, -1],
+}
+
+TEST_INPUT = """sesenwnenenewseeswwswswwnenewsewsw
+neeenesenwnwwswnenewnwwsewnenwseswesw
+seswneswswsenwwnwse
+nwnwneseeswswnenewneswwnewseswneseene
+swweswneswnenwsewnwneneseenw
+eesenwseswswnenwswnwnwsewwnwsene
+sewnenenenesenwsewnenwwwse
+wenwwweseeeweswwwnwwe
+wsweesenenewnwwnwsenewsenwwsesesenwne
+neeswseenwwswnwswswnw
+nenwswwsewswnenenewsenwsenwnesesenew
+enewnwewneswsewnwswenweswnenwsenwsw
+sweneswneswneneenwnewenewwneswswnese
+swwesenesewenwneswnwwneseswwne
+enesenwswwswneneswsenwnewswseenwsese
+wnwnesenesenenwwnenwsewesewsesesew
+nenewswnwewswnenesenwnesewesw
+eneswnwswnwsenenwnwnwwseeswneewsenese
+neswnwewnwnwseenwseesewsenwsweewe
+wseweeenwnesenwwwswnew""".splitlines()
+
+
+EXPECTED_PART_TWO_RESULTS = {
+    2: 12,
+    3: 25,
+    4: 14,
+    5: 23,
+    6: 28,
+    7: 41,
+    8: 37,
+    9: 49,
+    10: 37,
+    20: 132,
+    30: 259,
+    40: 406,
+    50: 566,
+    60: 788,
+    70: 1106,
+    80: 1373,
+    90: 1844,
+    100: 2208,
+}
+
+with open("day24.txt") as infile:
+    REAL_INPUT = [line.strip() for line in infile]
+
+
+def parse_step(line: str) -> Tuple[int, int, int]:
+    """Follow a step from start to finish"""
+    index = 0
+    start = (0, 0, 0)
+    while index < len(line):
+        if line[index] in MOVES:
+            x, y, z = start
+            x1, y1, z1 = MOVES[line[index]]
+            start = (x + x1, y + y1, z + z1)
+            index += 1
+        elif line[index : index + 2] in MOVES:
+            x, y, z = start
+            x1, y1, z1 = MOVES[line[index : index + 2]]
+            start = (x + x1, y + y1, z + z1)
+            index += 2
+        else:
+            raise ValueError(f"Unknown step {line[index:index + 2]}")
+    return start
+
+
+def part_one(puzzle: List[str]) -> int:
+    grid: Dict[Tuple[int], bool] = defaultdict(lambda: False)
+    for line in puzzle:
+        coordinates = parse_step(line)
+        grid[coordinates] = not grid[coordinates]
+    return sum(grid.values())
+
+
+def get_neighbor_coordinates(pos: Tuple[int, int, int]) -> List[Tuple[int, int, int]]:
+    result = []
+    x, y, z = pos
+    for x1, y1, z1 in MOVES.values():
+        result.append((x + x1, y + y1, z + z1))
+    return result
+
+
+def next_state(
+    pos: Tuple[int, int, int], grid: Dict[Tuple[int, int, int], bool]
+) -> bool:
+    neighbors = get_neighbor_coordinates(pos)
+    active_neighbors = sum(grid[neighbor] for neighbor in neighbors)
+    state = grid[pos]
+    if state:
+        if active_neighbors not in {1, 2}:
+            # if the tile is black and there are 0 or more than two active neighbors,
+            # flip it
+            state = False
+    else:
+        if active_neighbors == 2:
+            # if it's white and there are exactly two black tiles next to it, flip it
+            state = True
+    return state
+
+
+def take_turn(
+    grid: Dict[Tuple[int, int, int], bool]
+) -> Dict[Tuple[int, int, int], bool]:
+    x_values = sorted(grid)
+    y_values = sorted(grid, key=lambda k: k[1])
+    z_values = sorted(grid, key=lambda k: k[2])
+    min_x = x_values[0][0] - 1
+    max_x = x_values[-1][0] + 2
+    min_y = y_values[0][1] - 1
+    max_y = y_values[-1][1] + 2
+    min_z = z_values[0][2] - 1
+    max_z = z_values[-1][2] + 2
+    new_grid = defaultdict(lambda: False)
+    new_grid.update(
+        {
+            (x, y, z): next_state((x, y, z), grid)
+            for x in range(min_x, max_x)
+            for y in range(min_y, max_y)
+            for z in range(min_z, max_z)
+            # this conditional is crucial
+            if x + y + z == 0
+        }
+    )
+    return new_grid
+
+
+def part_two(puzzle: List[str], days: int = 100) -> int:
+    grid: Dict[Tuple[int], bool] = defaultdict(lambda: False)
+    for line in puzzle:
+        coordinates = parse_step(line)
+        grid[coordinates] = not grid[coordinates]
+    testing = puzzle == TEST_INPUT
+    for day in range(days):
+        grid = take_turn(grid)
+        if testing:
+            try:
+                expected_result = EXPECTED_PART_TWO_RESULTS[day + 1]
+            except KeyError:
+                pass
+            else:
+                assert expected_result == sum(grid.values()), (
+                    day + 1,
+                    sum(grid.values()),
+                    grid,
+                )
+        if not day % 10:
+            # this code gets slower as the days go on
+            print(f"in progress: day {day}")
+    return sum(grid.values())
+
+
+def main():
+    assert part_one(TEST_INPUT) == 10, part_one(TEST_INPUT)
+    print("part 1 result:", part_one(REAL_INPUT))
+    assert part_two(TEST_INPUT) == 2208, part_two(TEST_INPUT)
+    print("part 2 result", part_two(REAL_INPUT))
+
+
+if __name__ == "__main__":
+    main()