From 49d71606177166f8c3f8cee4e74fa669d2a83b7b Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 30 Dec 2024 23:58:21 -0500
Subject: [PATCH] 2018: d22: ex1: add solution

---
 2018/d22/ex1/ex1.py | 67 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100755 2018/d22/ex1/ex1.py

diff --git a/2018/d22/ex1/ex1.py b/2018/d22/ex1/ex1.py
new file mode 100755
index 0000000..c49e69d
--- /dev/null
+++ b/2018/d22/ex1/ex1.py
@@ -0,0 +1,67 @@
+#!/usr/bin/env python
+
+import enum
+import itertools
+import sys
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+class Region(enum.IntEnum):
+    ROCKY = 0
+    WET = 1
+    NARROW = 2
+
+
+def solve(input: str) -> int:
+    def parse(input: list[str]) -> tuple[int, Point]:
+        depth = input[0].removeprefix("depth: ")
+        target = input[1].removeprefix("target: ")
+        return int(depth), Point(*(int(n) for n in target.split(",")))
+
+    def compute_erosions(depth: int, target: Point) -> dict[Point, int]:
+        res: dict[Point, int] = {}
+        for x in range(0, target.x + 1):
+            for y in range(0, target.y + 1):
+                p = Point(x, y)
+                if p == Point(0, 0) or p == target:
+                    res[p] = 0
+                elif p.y == 0:
+                    res[p] = p.x * 16807
+                elif p.x == 0:
+                    res[p] = p.y * 48271
+                else:
+                    res[p] = res[Point(p.x - 1, p.y)] * res[Point(p.x, p.y - 1)]
+                # Go from geologic index to erosion level
+                res[p] += depth
+                res[p] %= 20183
+        return res
+
+    def compute_regions(depth: int, target: Point) -> dict[Point, Region]:
+        return {
+            p: Region(erosion % 3)
+            for p, erosion in compute_erosions(depth, target).items()
+        }
+
+    depth, target = parse(input.splitlines())
+    regions = compute_regions(depth, target)
+    return sum(
+        regions[p]
+        for p in map(
+            Point._make,
+            itertools.product(range(0, target.x + 1), range(target.y + 1)),
+        )
+    )
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()