97 lines
2.1 KiB
Python
97 lines
2.1 KiB
Python
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#!/usr/bin/env python
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import dataclasses
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import enum
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import sys
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from typing import NamedTuple
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def sign(n: int) -> int:
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if n > 0:
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return 1
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elif n < 0:
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return -1
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return 0
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class Direction(enum.Enum):
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UP = "U"
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DOWN = "D"
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LEFT = "L"
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RIGHT = "R"
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@dataclasses.dataclass
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class Move:
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dir: Direction
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len: int
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@classmethod
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def from_input(cls, line: str) -> "Move":
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d, l = line.split()
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return cls(Direction(d), int(l))
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class Point(NamedTuple):
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x: int
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y: int
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def move(self, direction: Direction) -> "Point":
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match direction:
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case Direction.UP:
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dx, dy = 1, 0
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case Direction.DOWN:
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dx, dy = -1, 0
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case Direction.LEFT:
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dx, dy = 0, -1
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case Direction.RIGHT:
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dx, dy = 0, 1
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return Point(self.x + dx, self.y + dy)
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@dataclasses.dataclass
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class Rope:
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points: list[Point] = dataclasses.field(init=False)
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_tail_positions: set[Point] = dataclasses.field(init=False)
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def __init__(self, *, length: int = 2) -> None:
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assert length > 0
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self.points = [Point(0, 0)] * length
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self._tail_positions = {self.points[-1]}
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def move(self, move: Move) -> None:
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for _ in range(move.len):
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self.points[0] = self.points[0].move(move.dir)
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for i in range(1, len(self.points)):
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self.points[i] = self.__move_tail(self.points[i - 1], self.points[i])
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self._tail_positions.add(self.points[-1])
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@staticmethod
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def __move_tail(head: Point, tail: Point) -> Point:
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delta_x, delta_y = head.x - tail.x, head.y - tail.y
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if abs(delta_x) <= 1 and abs(delta_y) <= 1:
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return tail
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dx, dy = sign(delta_x), sign(delta_y)
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return Point(tail.x + dx, tail.y + dy)
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def solve(input: list[str]) -> int:
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moves = map(Move.from_input, input)
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rope = Rope(length=2)
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for move in moves:
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rope.move(move)
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return len(rope._tail_positions)
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def main() -> None:
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input = sys.stdin.read().splitlines()
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print(solve(input))
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if __name__ == "__main__":
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main()
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