Day 22.

22.py

@@ -0,0 +1,64 @@
+import operator
+from collections import defaultdict
+from enum import Enum
+
+
+class State(Enum):
+    clean = 0,
+    weakened = 1,
+    infected = 2,
+    flagged = 3
+
+
+def clean_cells():
+    cells = defaultdict(lambda: State.clean)
+    for y, line in enumerate(lines):
+        for x, c in enumerate(line):
+            cells[(x, y)] = State.infected if c == '#' else State.clean
+    return cells
+
+
+def execute(runs, transitions):
+    cells, location, direction, infected = clean_cells(), start, (0, -1), 0
+    for _ in range(runs):
+        direction = directions[cells[location]][direction]
+        cells[location] = transitions[cells[location]]
+        if cells[location] == State.infected:
+            infected += 1
+        location = tuple(map(operator.add, location, direction))
+    return infected
+
+
+with open('data/22.txt') as file:
+    lines = file.readlines()
+    start = ((len(lines[0]) - 1) // 2, (len(lines) - 1) // 2)
+
+    right = {(0, -1): (1, 0), (1, 0): (0, 1), (0, 1): (-1, 0), (-1, 0): (0, -1)}
+    left = {v: k for k, v in right.items()}
+    identity = {v: v for v in right.values()}
+    reverse = {v: (-1 * v[0], -1 * v[1]) for v in right.values()}
+
+    directions = {
+        State.clean: left,
+        State.infected: right,
+        State.weakened: identity,
+        State.flagged: reverse
+    }
+
+    transitions = [
+        {
+            # part one
+            State.clean: State.infected,
+            State.infected: State.clean,
+        },
+        {
+            # part two
+            State.clean: State.weakened,
+            State.weakened: State.infected,
+            State.infected: State.flagged,
+            State.flagged: State.clean,
+        }
+    ]
+
+    print(f'Part one: {execute(10000, transitions[0])}')
+    print(f'Part two: {execute(10000000, transitions[1])}')

data/22.txt

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+...##.#.#.####...###.....
+..#..##.#...#.##.##.#..#.
+.#.#.#.###....#...###....
+.#....#..####.....##.#..#
+##.#.#.#.#..#..#.....###.
+#...##....##.##.#.##.##..
+.....###..###.###...#####
+######.####..#.#......##.
+#..###.####..####........
+#..######.##....####...##
+...#.##.#...#.#.#.#..##.#
+####.###..#####.....####.
+#.#.#....#.####...####...
+##...#..##.##....#...#...
+......##..##..#..#..####.
+.##..##.##..####..##....#
+.#..#..##.#..##..#...#...
+#.#.##.....##..##.#####..
+##.#.......#....#..###.#.
+##...#...#....###..#.#.#.
+#....##...#.#.#.##..#..##
+#..#....#####.....#.##.#.
+.#...#..#..###....###..#.
+..##.###.#.#.....###.....
+#.#.#.#.#.##.##...##.##.#