From affaf6e96f217c3225e6f8bfcf833c6b1af98d43 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Thu, 28 Oct 2021 17:54:52 +0200
Subject: [PATCH] 2019 day 24 part 1

---
 2019/aoc2019/day24.py    | 58 ++++++++++++++++++++++++++++++++++++
 2019/tests/test_day24.py | 64 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 2019/aoc2019/day24.py
 create mode 100644 2019/tests/test_day24.py

diff --git a/2019/aoc2019/day24.py b/2019/aoc2019/day24.py
new file mode 100644
index 0000000..9dced01
--- /dev/null
+++ b/2019/aoc2019/day24.py
@@ -0,0 +1,58 @@
+from typing import TextIO, Iterable, Tuple
+
+
+def read_board(data: TextIO) -> Tuple[Tuple[bool]]:
+    return tuple(
+        tuple(c == '#' for c in line.strip())
+        for line in data
+    )
+
+
+def flatten(it: Iterable[Iterable]) -> Iterable:
+    for item in it:
+        yield from item
+
+
+def neighbours(board: Tuple[Tuple[bool]], x: int, y: int) -> int:
+    n = 0
+
+    if x > 0 and board[y][x - 1]:
+        n += 1
+
+    if x + 1 < len(board[0]) and board[y][x + 1]:
+        n += 1
+
+    if y > 0 and board[y - 1][x]:
+        n += 1
+
+    if y + 1 < len(board) and board[y + 1][x]:
+        n += 1
+
+    return n
+
+
+def advance_board(board: Tuple[Tuple[bool]]) -> Tuple[Tuple[bool]]:
+    def create_row(y: int, row: Tuple[bool]):
+        new_row = []
+        for x, live in enumerate(row):
+            if live:
+                new_row.append(neighbours(board, x, y) == 1)
+            else:
+                new_row.append(neighbours(board, x, y) in [1, 2])
+
+        return tuple(new_row)
+
+    return tuple(create_row(y, row) for y, row in enumerate(board))
+
+
+def part1(data: TextIO) -> int:
+    board = read_board(data)
+
+    seen = set(board)
+
+    while True:
+        board = advance_board(board)
+        if board in seen:
+            return sum(2 ** i for i, b in enumerate(flatten(board)) if b)
+
+        seen.add(board)
diff --git a/2019/tests/test_day24.py b/2019/tests/test_day24.py
new file mode 100644
index 0000000..51426b0
--- /dev/null
+++ b/2019/tests/test_day24.py
@@ -0,0 +1,64 @@
+import io
+
+import pytest
+
+from aoc2019.day24 import read_board, advance_board, part1
+
+SAMPLE_START = """\
+....#
+#..#.
+#..##
+..#..
+#....
+"""
+
+SAMPLE_STATES = """\
+....#
+#..#.
+#..##
+..#..
+#....
+
+#..#.
+####.
+###.#
+##.##
+.##..
+
+#####
+....#
+....#
+...#.
+#.###
+
+#....
+####.
+...##
+#.##.
+.##.#
+
+####.
+....#
+##..#
+.....
+##...
+""".split("\n\n")
+
+
+@pytest.mark.parametrize("cycles,state", enumerate(SAMPLE_STATES))
+def test_evolution_part1(cycles: int, state: str) -> None:
+    with io.StringIO(SAMPLE_START) as f:
+        board = read_board(f)
+
+    with io.StringIO(state) as f:
+        final_state = read_board(f)
+
+    for _ in range(cycles):
+        board = advance_board(board)
+
+    assert board == final_state
+
+
+def test_sample_part1() -> None:
+    with io.StringIO(SAMPLE_START) as f:
+        assert part1(f) == 2129920