2024: Day 18 - Part 1

Author: MiLk

2024/python/day18/__init__.py

@@ -0,0 +1,42 @@
+from collections.abc import Iterable, Container
+
+from utils.file import read_input, int_list_line
+
+falling_bytes = [complex(x,y) for x,y in (int_list_line(line, ",") for line in read_input(__package__))]
+start = 0j
+goal = 70+70j if len(falling_bytes) > 50 else 6+6j
+
+def neighbors(node: complex, walls: Container[complex]) -> Iterable[complex]:
+    for direction in [1, -1, 1j, -1j]:
+        neighbor = node + direction
+        if neighbor.real < 0 or neighbor.imag < 0 or neighbor.real > goal.real or neighbor.imag > goal.imag:
+            continue
+        if neighbor not in walls:
+            yield neighbor
+
+def heuristic(node: complex, goal: complex) -> int:
+    return int(abs(node.real - goal.real) + abs(node.imag - goal.imag)) + int(abs(node.real - node.imag))
+
+def walk(corruption_size: int) -> Iterable[tuple[list[complex], int]]:
+    corrupted = set(falling_bytes[:corruption_size])
+    best_score = None
+    visited = {start: 0}
+    # position, score, path
+    stack: list[tuple[complex, int, list[complex]]] = [(start, 0, [start])]
+    while stack:
+        stack.sort(key=lambda x: x[1] + heuristic(x[0], goal))
+        node, score, path = stack.pop()
+        if score > best_score:
+            continue
+        visited[node] = score if node not in visited else min(score, visited[node])
+        for neighbor in neighbors(node, corrupted):
+            new_score = score + 1
+            if neighbor == goal:
+                #print("Path found", new_score, len(stack))
+                best_score = min(best_score, new_score) if best_score else new_score
+                yield path + [neighbor], new_score
+            if neighbor not in visited or new_score < visited[neighbor]:
+                stack.append((neighbor, new_score, path + [neighbor]))
+
+paths = list(walk(1024))
+print("Part 1:", min(score for path, score in paths))