From 137a98e936e729ee7e8b91ac3369c2225fe27848 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Thu, 9 Dec 2021 12:57:23 +0100
Subject: [PATCH] 2021: d09: ex1: add solution

---
 2021/d09/ex1/ex1.py | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100755 2021/d09/ex1/ex1.py

diff --git a/2021/d09/ex1/ex1.py b/2021/d09/ex1/ex1.py
new file mode 100755
index 0000000..e84e893
--- /dev/null
+++ b/2021/d09/ex1/ex1.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+
+import sys
+from typing import Iterator, List, Tuple
+
+HeightMap = List[List[int]]
+Point = Tuple[int, int]
+
+
+def solve(input: List[str]) -> int:
+    height_map = [[int(c) for c in line] for line in input]
+
+    def neighbours_of(point: Point) -> Iterator[Point]:
+        for dx, dy in (-1, 0), (1, 0), (0, -1), (0, 1):
+            x, y = point[0] + dx, point[1] + dy
+            if x < 0 or x >= len(height_map):
+                continue
+            if y < 0 or y >= len(height_map[0]):
+                continue
+            yield x, y
+
+    def is_low_point(point: Point) -> bool:
+        for neighbour in neighbours_of(point):
+            if height_map[neighbour[0]][neighbour[1]] <= height_map[point[0]][point[1]]:
+                return False
+        return True
+
+    def risk_level(point: Point) -> int:
+        return 1 + height_map[point[0]][point[1]]
+
+    points = [(x, y) for x in range(len(height_map)) for y in range(len(height_map[0]))]
+    return sum(risk_level(p) for p in points if is_low_point(p))
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()