From 20784cb2ca050e3fe2ecb32c674f083274b3b0a7 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 20 Dec 2020 14:27:02 +0100
Subject: [PATCH] 2020: d20: ex2: add solution

---
 2020/d20/ex2/ex2.py | 185 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 185 insertions(+)
 create mode 100755 2020/d20/ex2/ex2.py

diff --git a/2020/d20/ex2/ex2.py b/2020/d20/ex2/ex2.py
new file mode 100755
index 0000000..e923806
--- /dev/null
+++ b/2020/d20/ex2/ex2.py
@@ -0,0 +1,185 @@
+#!/usr/bin/env python
+
+import functools
+import itertools
+import math
+import sys
+from collections import defaultdict
+from copy import deepcopy
+from typing import Dict, Iterator, List, Set, Tuple
+
+Tile = List[List[str]]
+Tiles = Dict[int, Tile]
+
+
+def parse(raw: str) -> Tiles:
+    def parse_tile(raw: List[str]) -> Tile:
+        return [[line[i] for i in range(len(line))] for line in raw]
+
+    res = {}
+    for lines in map(lambda s: s.splitlines(), raw.split("\n\n")):
+        if len(lines) == 0:
+            continue
+        nums = int(lines[0][5:-1])
+        res[nums] = parse_tile(lines[1:])
+    return res
+
+
+def rotations(tile: Tile) -> Iterator[Tile]:
+    yield tile
+    for __ in range(3):
+        tile = [
+            [tile[j][i] for j in range(len(tile))]
+            for i in range(len(tile[0]) - 1, -1, -1)
+        ]
+        yield tile
+
+
+def flips(tile: Tile) -> Iterator[Tile]:
+    yield tile
+    yield tile[::-1]
+    yield [line[::-1] for line in tile]
+    yield [line[::-1] for line in tile[::-1]]
+
+
+def transforms(tile: Tile) -> List[Tile]:
+    # Can't use a set with lists...
+    res: List[Tile] = functools.reduce(
+        lambda l, it: l + [it] if not any(it == other for other in l) else l,
+        itertools.chain.from_iterable(map(rotations, flips(tile))),
+        [],
+    )
+    return res
+
+
+def borders(tile: Tile) -> Iterator[str]:
+    # They should match on same axis (i.e: go clockwise and counter-clockwise)
+    return map(
+        lambda s: "".join(s),
+        [
+            tile[0],
+            [line[-1] for line in tile],
+            tile[-1],
+            [line[0] for line in tile],
+        ],
+    )
+
+
+Transforms = Dict[int, List[Tile]]
+Tiling = List[List[Tuple[int, int]]]  # Which tile, and which transform
+
+
+def build_tiling(tiles: Tiles) -> Tuple[Transforms, Tiling]:
+    transform_mapping = {num: transforms(tile) for num, tile in tiles.items()}
+    trans_borders: Dict[int, Dict[int, List[str]]] = defaultdict(dict)
+    for num, trans in transform_mapping.items():
+        for i, t in enumerate(trans):
+            trans_borders[num][i] = list(borders(t))
+    length = math.isqrt(len(tiles))
+    tiling = [[(-1, -1)] * length for __ in range(length)]
+
+    def rec(x: int = 0, y: int = 0, used: Set[int] = set()) -> bool:
+        if x == length:
+            return True
+        for num, borders in trans_borders.items():
+            if num in used:
+                continue
+            used |= {num}
+
+            for trans, border in borders.items():
+                top, __, __, left = border
+                if y > 0:
+                    nid, ntrans = tiling[x][y - 1]
+                    __, right, __, __ = trans_borders[nid][ntrans]
+                    if left != right:
+                        continue
+                if x > 0:
+                    nid, ntrans = tiling[x - 1][y]
+                    __, __, bottom, __ = trans_borders[nid][ntrans]
+                    if top != bottom:
+                        continue
+                tiling[x][y] = num, trans
+
+                next_x, next_y = (x, y + 1) if y < (length - 1) else (x + 1, 0)
+                if rec(next_x, next_y, used):
+                    return True
+
+            used -= {num}
+
+        tiling[x][y] = (-1, -1)
+        return False
+
+    assert rec()
+    return transform_mapping, tiling
+
+
+def trim(trans: Transforms, tiling: Tiling) -> Tile:
+    def trim_tile(tile: Tile) -> Tile:
+        return [line[1:-1] for line in tile[1:-1]]
+
+    def tiling_to_tile(tiling: List[List[Tile]]) -> Tile:
+        res: Tile = []
+        for i in range(len(tiling) * len(tiling[0][0])):
+            res.append([])
+            tile_line_idx = i % len(tiling[0][0])
+            for j in range(len(tiling[0]) * len(tiling[0][0][0])):
+                tile = tiling[i // len(tiling[0][0])][j // len(tiling[0][0][0])]
+                tile_row_idx = j % len(tiling[0][0][0])
+                res[-1].append(tile[tile_line_idx][tile_row_idx])
+        return res
+
+    tiles = [[trim_tile(trans[num][id]) for num, id in line] for line in tiling]
+    return tiling_to_tile(tiles)
+
+
+def find_monster(image: Tile, monster: Tile) -> Iterator[Tuple[int, int]]:
+    def monster_at(x: int, y: int) -> bool:
+        for i in range(len(monster)):
+            for j in range(len(monster[0])):
+                if monster[i][j] == " ":
+                    continue
+                if image[x + i][y + j] != "#":
+                    return False
+        return True
+
+    # Returns upper left corner if found
+    for i in range(len(image) - len(monster)):
+        for j in range(len(image[0]) - len(monster[0])):
+            if monster_at(i, j):
+                yield i, j
+
+
+def remove_monster(image: Tile, monster: Tile, x: int, y: int) -> None:
+    for i in range(len(monster)):
+        for j in range(len(monster[0])):
+            if monster[i][j] == " ":
+                continue
+            image[x + i][y + j] = " "
+
+
+def solve(tiles: Tiles) -> int:
+    image = trim(*build_tiling(tiles))
+    monster = [
+        [char for char in line]
+        for line in (
+            "                  # ",
+            "#    ##    ##    ###",
+            " #  #  #  #  #  #   ",
+        )
+    ]
+    monsters = transforms(monster)
+
+    for monster in monsters:
+        for coords in find_monster(image, monster):
+            remove_monster(image, monster, *coords)
+
+    return sum(sum(char == "#" for char in line) for line in image)
+
+
+def main() -> None:
+    input = parse(sys.stdin.read())
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()