Implement 2024 day 16 part 1

2024/src/aoc/days/day16.py

@@ -0,0 +1,56 @@
+import heapq
+
+import numpy
+
+from . import SeparateRunner
+
+TURNS = (
+    (-1, 1),
+    (1, -1),
+)
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, input: str) -> int:
+        grid = numpy.array([list(line) for line in input.strip().split("\n")])
+
+        y, x = numpy.where(grid == "S")
+        x, y = x[0], y[0]
+
+        todo = [(0, x, y, 1, 0)]
+        best = {
+            (x, y, 1, 0): 0,
+        }
+
+        def enqueue(dist, x, y, dx, dy):
+            if grid[y, x] == "#":
+                return
+
+            if (x, y, dx, dy) not in best or best[x, y, dx, dy] > dist:
+                best[x, y, dx, dy] = dist
+                heapq.heappush(todo, (dist, x, y, dx, dy))
+
+        while todo:
+            dist, x, y, dx, dy = heapq.heappop(todo)
+
+            if best[x, y, dx, dy] < dist:
+                continue
+
+            if grid[y, x] == "E":
+                return dist
+
+            enqueue(dist + 1, x + dx, y + dy, dx, dy)
+            enqueue(dist + 2001, x - dx, y - dy, dx, dy)
+
+            for tx, ty in TURNS:
+                ndx = dy * ty
+                ndy = dx * ty
+
+                enqueue(dist + 1001, x + ndx, y + ndy, ndx, ndy)
+
+        raise ValueError("Did not find path to exit")
+
+    @classmethod
+    def part2(cls, input: str) -> int:
+        pass