2017: d11: ex2: add solution

2017/d11/ex2/ex2.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+import enum
+import sys
+from collections.abc import Iterator
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+class Direction(enum.StrEnum):
+    NORTH_WEST = "nw"
+    NORTH = "n"
+    NORTH_EAST = "ne"
+    SOUTH_EAST = "se"
+    SOUTH = "s"
+    SOUTH_WEST = "sw"
+
+    # https://www.redblobgames.com/grids/hexagons/#coordinates-axial
+    def apply(self, p: Point) -> Point:
+        # (x, y) <=> (q, r)
+        match self:
+            case Direction.NORTH_WEST:
+                dx, dy = -1, 0
+            case Direction.NORTH:
+                dx, dy = 0, -1
+            case Direction.NORTH_EAST:
+                dx, dy = 1, -1
+            case Direction.SOUTH_EAST:
+                dx, dy = 1, 0
+            case Direction.SOUTH:
+                dx, dy = 0, 1
+            case Direction.SOUTH_WEST:
+                dx, dy = -1, 1
+        return Point(p.x + dx, p.y + dy)
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[Direction]:
+        return [Direction(dir) for dir in input.strip().split(",")]
+
+    # https://www.redblobgames.com/grids/hexagons/#distances-axial
+    def hex_dist(a: Point, b: Point) -> int:
+        dx, dy = a.x - b.x, a.y - b.y
+        return (abs(dx) + abs(dx + dy) + abs(dy)) // 2
+
+    def walk(directions: list[Direction]) -> Iterator[Point]:
+        pos = Point(0, 0)
+        for dir in directions:
+            pos = dir.apply(pos)
+            yield pos
+
+    directions = parse(input)
+    return max(hex_dist(p, Point(0, 0)) for p in walk(directions))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()