2020: d05: ex2: add solution

2020/d05/ex2/ex2.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+
+import sys
+from typing import List
+
+
+def seat_id(boarding_pass: str) -> int:
+    min_x = 0
+    max_x = 128
+    min_y = 0
+    max_y = 8
+
+    for char in boarding_pass:
+        if char == "F":
+            max_x = (min_x + max_x) // 2
+        elif char == "B":
+            min_x = (min_x + max_x) // 2
+        elif char == "L":
+            max_y = (min_y + max_y) // 2
+        elif char == "R":
+            min_y = (min_y + max_y) // 2
+    return min_x * 8 + min_y
+
+
+def solve(passes: List[str]) -> int:
+    ids = sorted(seat_id(p) for p in passes)
+
+    for prev, cur in zip(ids, ids[1:]):
+        if prev + 1 != cur:
+            return prev + 1
+
+    assert False  # Sanity check
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()