2024: Day 12 - Part 1

Author: MiLk

2024/python/day12/__init__.py

@@ -0,0 +1,42 @@
+from operator import attrgetter, itemgetter
+
+from utils.file import read_input
+
+plots = {complex(x, y): c for y, line in enumerate(read_input(__package__)) for x, c in enumerate(line)}
+
+
+def flood(start: complex) -> tuple[str, set[complex]]:
+    region_name = plots[start]
+    visited: set[complex] = set()
+    queue: list[complex] = [start]
+    while queue:
+        current = queue.pop()
+        if current in visited or plots.get(current) != region_name:
+            continue
+        visited.add(current)
+        queue.extend(current + d for d in {-1, 1, -1j, 1j})
+    return region_name, visited
+
+
+def perimeter(region: set[complex]) -> int:
+    return sum(plot + d not in region for plot in region for d in {-1, 1, -1j, 1j})
+
+
+def find_regions() -> list[tuple[str, set[complex]]]:
+    visited_plots: set[complex] = set()
+    result: list[tuple[str, set[complex]]] = []
+
+    sorted_plots = sorted(plots, key=lambda p: (p.real, p.imag))
+    while sorted_plots:
+        current = sorted_plots.pop()
+        if current in visited_plots:
+            continue
+        name, region = flood(current)
+        visited_plots |= region
+        result.append((name, region))
+
+    return result
+
+
+regions = find_regions()
+print("Part1:", sum(perimeter(region) * len(region) for _, region in regions))