2017: d13: ex2: add solution

2017/d13/ex2/ex2.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> dict[int, int]:
+        return {
+            depth: range
+            for depth, range in (map(int, l.split(": ")) for l in input.splitlines())
+        }
+
+    def would_catch(depth: int, range: int, offset: int) -> bool:
+        cycle_length = (range - 1) * 2
+        return (depth + offset) % cycle_length == 0
+
+    def compute_delay(firewall: dict[int, int]) -> int:
+        for i in itertools.count():
+            if any(would_catch(depth, range, i) for depth, range in firewall.items()):
+                continue
+            return i
+        assert False  # Sanity check
+
+    firewall = parse(input)
+    return compute_delay(firewall)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()