2016: d18: ex1: add solution

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()