Day 8: Resonant Collinearity

README.md

@@ -12,4 +12,4 @@ Development occurs in language-specific directories:
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
 |[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)|[day7.rs](rs/src/day7.rs)|
-|[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|||
+|[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)||

py/aoc2024/day8.py

@@ -0,0 +1,70 @@
+"""
+Day 8: Resonant Collinearity
+"""
+
+from collections import defaultdict
+from collections.abc import Iterable
+from itertools import count
+
+SAMPLE_INPUT = """
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+"""
+
+
+class _Count(Iterable[int]):
+    def __iter__(self):
+        return count()
+
+
+def _solve(data: str, multiples: Iterable[int]) -> int:
+    lines = data.strip("\n").splitlines()
+    height = len(lines)
+    width = height and max(map(len, lines))
+    antennae = defaultdict(list)
+    for y, line in enumerate(lines):
+        for x, char in enumerate(line):
+            if char != ".":
+                antennae[char].append((y, x))
+    antinodes = set()
+    for points in antennae.values():
+        for y0, x0 in points:
+            for y1, x1 in points:
+                if y0 == y1 and x0 == x1:
+                    continue
+                dy, dx = y1 - y0, x1 - x0
+                for i in multiples:
+                    y2, x2 = y1 + i * dy, x1 + i * dx
+                    if y2 not in range(height) or x2 not in range(width):
+                        break
+                    antinodes.add((y2, x2))
+    return len(antinodes)
+
+
+def part1(data: str) -> int:
+    """
+    >>> part1(SAMPLE_INPUT)
+    14
+    """
+    return _solve(data, (1,))
+
+
+def part2(data: str) -> int:
+    """
+    >>> part2(SAMPLE_INPUT)
+    34
+    """
+    return _solve(data, _Count())
+
+
+parts = (part1, part2)

py/pyproject.toml

@@ -31,6 +31,7 @@ day4 = "aoc2024.day4:parts"
 day5 = "aoc2024.day5:parts"
 day6 = "aoc2024.day6:parts"
 day7 = "aoc2024.day7:parts"
+day8 = "aoc2024.day8:parts"
 
 [build-system]
 requires = ["poetry-core"]