Implement 2024 day 8

2024/src/aoc/days/day8.py

@@ -0,0 +1,60 @@
+import itertools
+import math
+from collections import defaultdict
+
+import numpy
+
+from . import CombinedRunner
+
+
+def simplify(vec: numpy.array) -> numpy.array:
+    if vec[0] == 0:
+        return numpy.array([0, 1])
+    elif vec[1] == 0:
+        return numpy.array([0, 1])
+    else:
+        div = math.gcd(*vec)
+        return vec // div
+
+
+class DayRunner(CombinedRunner):
+    @classmethod
+    def run_both(cls, input: str) -> int:
+        grid = input.strip().split("\n")
+        height = len(grid)
+        width = len(grid[0])
+
+        antennae = defaultdict(list)
+
+        for y, line in enumerate(grid):
+            for x, c in enumerate(line):
+                if c != ".":
+                    antennae[c].append(numpy.array([x, y]))
+
+        antinodes = set()
+        antinodes2 = set()
+
+        def in_bounds(node: numpy.array) -> bool:
+            return 0 <= node[0] < width and 0 <= node[1] < height
+
+        def add(node: numpy.array):
+            if in_bounds(node):
+                antinodes.add(tuple(node))
+
+        def walk(start: numpy.array, step: numpy.array):
+            for pos in itertools.count(start, step):
+                if in_bounds(pos):
+                    antinodes2.add(tuple(pos))
+                else:
+                    break
+
+        for values in antennae.values():
+            for a, b in itertools.combinations(values, 2):
+                add(2 * a - b)
+                add(2 * b - a)
+
+                step = simplify(b - a)
+                walk(b, step)
+                walk(a, -step)
+
+        return len(antinodes), len(antinodes2)