2024.08

challenges/2024/08-resonantCollinearity/README.md

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+# [Day 8: Resonant Collinearity](https://adventofcode.com/2024/day/8)
+
+Part 1 is:
+* less than 298
+
+This is not a fully generic solution as, in a situation where the differences between x and y dimensions of pairs of coordinates are not coprime, this implementation would skip steps.

challenges/2024/08-resonantCollinearity/main.py

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+import sys
+from gridutil import grid, coord
+from collections import defaultdict
+import itertools
+from fractions import Fraction
+
+
+def parse(instr: str) -> tuple[dict[str, list[coord.Coordinate]], tuple[int, int]]:
+    g = grid.parse(instr)
+    antenna_by_type = defaultdict(list)
+    for key in g:
+        if g[key] == ".":
+            continue
+        antenna_by_type[g[key]].append(key)
+    return antenna_by_type, (grid.get_max_x(g), grid.get_max_y(g))
+
+
+def one(instr: str):
+    (antenna_by_type, (max_x, max_y)) = parse(instr)
+
+    pos = set()
+    for antenna_type in antenna_by_type:
+        for (a, b) in itertools.permutations(antenna_by_type[antenna_type], 2):
+            diff = coord.sub(b, a)
+            c = coord.add(a, coord.mult(diff, 2))
+            if 0 <= c.x <= max_x and 0 <= c.y <= max_y:
+                pos.add(c)
+
+    return len(pos)
+
+
+def two(instr: str):
+    (antenna_by_type, (max_x, max_y)) = parse(instr)
+
+    pos = set()
+    for antenna_type in antenna_by_type:
+        for (a, b) in itertools.permutations(antenna_by_type[antenna_type], 2):
+            if (
+                a.x > b.x
+            ):  # filter out (most) duplicate pairs eg ((1, 2), (2, 1)) will only be calculated as ((2, 1), (1, 2)) will be filtered. This also prevents diff.x from being negative (useful for the mod operation)
+                continue
+
+            diff = coord.sub(b, a)
+
+            m = Fraction(
+                diff.y, diff.x
+            )  # equiv of diff.y / diff.x but without the 26.9999999999996 issue
+            c = a.y - (m * a.x)
+
+            x_cursor = a.x % diff.x
+            y_cursor = int((x_cursor * m) + c)
+            while x_cursor <= max_x:
+                if 0 <= y_cursor <= max_y:
+                    pos.add((x_cursor, y_cursor))
+                x_cursor += diff.x
+                y_cursor += diff.y
+
+    return len(pos)
+
+
+def _debug(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print(*args, **kwargs)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2 or sys.argv[1] not in ["1", "2"]:
+        print("Missing day argument", file=sys.stderr)
+        sys.exit(1)
+    inp = sys.stdin.read().strip()
+    if sys.argv[1] == "1":
+        print(one(inp))
+    else:
+        print(two(inp))

challenges/2024/08-resonantCollinearity/tests.json

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+{
+    "1": [
+        {
+            "is": "14",
+            "input": "............\n........0...\n.....0......\n.......0....\n....0.......\n......A.....\n............\n............\n........A...\n.........A..\n............\n............\n\n"
+        },
+        {
+            "is": "2",
+            "input": "..........\n..........\n..........\n....a.....\n..........\n.....a....\n..........\n..........\n..........\n..........\n\n"
+        },
+        {
+            "is": "4",
+            "input": "..........\n..........\n..........\n....a.....\n........a.\n.....a....\n..........\n..........\n..........\n..........\n"
+        }
+    ],
+    "2": [
+        {
+            "is": "34",
+            "input": "............\n........0...\n.....0......\n.......0....\n....0.......\n......A.....\n............\n............\n........A...\n.........A..\n............\n............\n\n"
+        },
+        {
+            "is": "9",
+            "input": "T.........\n...T......\n.T........\n..........\n..........\n..........\n..........\n..........\n..........\n..........\n"
+        }
+    ]
+}