From 5bf73d5948213f39c2f456ecb5abf5d8712cc750 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 19 May 2025 22:31:02 +0100
Subject: [PATCH] 2016: d18: ex1: add solution

---
 2016/d18/ex1/ex1.py | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100755 2016/d18/ex1/ex1.py

diff --git a/2016/d18/ex1/ex1.py b/2016/d18/ex1/ex1.py
new file mode 100755
index 0000000..b02801b
--- /dev/null
+++ b/2016/d18/ex1/ex1.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+
+import sys
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> set[int]:
+        return {i for i, c in enumerate(input.strip()) if c == "^"}
+
+    def is_trap(tile: int, traps: set[int]) -> bool:
+        match ((tile - 1) in traps, tile in traps, (tile + 1) in traps):
+            case (True, True, False):
+                return True
+            case (False, True, True):
+                return True
+            case (True, False, False):
+                return True
+            case (False, False, True):
+                return True
+            case _:
+                return False
+
+    def step_row(traps: set[int], row_length: int) -> set[int]:
+        return {i for i in range(row_length) if is_trap(i, traps)}
+
+    traps = parse(input)
+    row_length = len(input.strip())
+    safe_tiles = row_length - len(traps)
+    for _ in range(40 - 1):
+        traps = step_row(traps, row_length)
+        safe_tiles += row_length - len(traps)
+    return safe_tiles
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()