2016: d01: ex2: add solution

2016/d01/ex2/ex2.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python
+
+import enum
+import sys
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+class Direction(enum.Enum):
+    NORTH = Point(-1, 0)
+    EAST = Point(0, 1)
+    SOUTH = Point(1, 0)
+    WEST = Point(0, -1)
+
+    def left(self) -> "Direction":
+        match self:
+            case Direction.NORTH:
+                return Direction.WEST
+            case Direction.EAST:
+                return Direction.NORTH
+            case Direction.SOUTH:
+                return Direction.EAST
+            case Direction.WEST:
+                return Direction.SOUTH
+
+    def right(self) -> "Direction":
+        match self:
+            case Direction.NORTH:
+                return Direction.EAST
+            case Direction.EAST:
+                return Direction.SOUTH
+            case Direction.SOUTH:
+                return Direction.WEST
+            case Direction.WEST:
+                return Direction.NORTH
+
+    def apply(self, p: Point, n: int = 1) -> Point:
+        dx, dy = self.value
+        return Point(p.x + dx * n, p.y + dy * n)
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[tuple[str, int]]:
+        return [((line[0]), int(line[1:])) for line in input.split(", ")]
+
+    def first_repeat(directions: list[tuple[str, int]]) -> Point:
+        pos, dir = Point(0, 0), Direction.NORTH
+        directions = parse(input)
+        seen = {pos}
+        for turn, length in directions:
+            dir = dir.left() if turn == "L" else dir.right()
+            for _ in range(length):
+                pos = dir.apply(pos)
+                if pos in seen:
+                    return pos
+                seen.add(pos)
+        assert False  # Sanity check
+
+    directions = parse(input)
+    pos = first_repeat(directions)
+    return abs(pos.x) + abs(pos.y)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()