part_a.py

#!/usr/bin/env python3
import functools

import utils


class Challenge(utils.BaseChallenge):
    def solve(self, _input, debug=False):
        """
        >>> Challenge().default_solve()
        187
        """
        return TreeMap.from_text(_input)\
            .get_tree_count_on_slope((3, 1))


class TreeMap:
    PARSE_MAP = {
        '.': False,
        '#': True,
    }

    @classmethod
    def from_text(cls, tree_map_text):
        """
        >>> TreeMap.from_text(
        ...     "..#\\n"
        ...     "#..\\n"
        ...     ".#.\\n"
        ... ).lines
        [[False, False, True], [True, False, False], [False, True, False]]
        """
        lines = tree_map_text.splitlines()
        non_empty_lines = filter(None, lines)
        return cls([
            list(map(cls.PARSE_MAP.__getitem__, line))
            for line in non_empty_lines
        ])

    def __init__(self, lines):
        self.lines = lines
        if self.lines:
            self.line_length = len(self.lines[0])
        else:
            self.line_length = None

    def get_product_of_tree_counts_on_slopes(self, slopes):
        """
        >>> tree_map_b = TreeMap.from_text(
        ...     "..##.......\\n"
        ...     "#...#...#..\\n"
        ...     ".#....#..#.\\n"
        ...     "..#.#...#.#\\n"
        ...     ".#...##..#.\\n"
        ...     "..#.##.....\\n"
        ...     ".#.#.#....#\\n"
        ...     ".#........#\\n"
        ...     "#.##...#...\\n"
        ...     "#...##....#\\n"
        ...     ".#..#...#.#\\n"
        ... )
        >>> tree_map_b.get_product_of_tree_counts_on_slopes(
        ...     [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)])
        336
        """
        return functools.reduce(int.__mul__, (
            self.get_tree_count_on_slope(slope)
            for slope in slopes
        ), 1)

    def get_tree_counts_on_slopes(self, slopes):
        """
        >>> tree_map_b = TreeMap.from_text(
        ...     "..##.......\\n"
        ...     "#...#...#..\\n"
        ...     ".#....#..#.\\n"
        ...     "..#.#...#.#\\n"
        ...     ".#...##..#.\\n"
        ...     "..#.##.....\\n"
        ...     ".#.#.#....#\\n"
        ...     ".#........#\\n"
        ...     "#.##...#...\\n"
        ...     "#...##....#\\n"
        ...     ".#..#...#.#\\n"
        ... )
        >>> tree_map_b.get_tree_counts_on_slopes(
        ...     [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)])
        [2, 7, 3, 4, 2]
        """
        return [
            self.get_tree_count_on_slope(slope)
            for slope in slopes
        ]

    def get_tree_count_on_slope(self, slope):
        """
        >>> TreeMap([[False] * 3] * 3).get_tree_count_on_slope((1, 1))
        0
        >>> TreeMap([[True] * 3] * 3).get_tree_count_on_slope((1, 1))
        3
        >>> tree_map_a = TreeMap.from_text(
        ...     "..#\\n"
        ...     "#..\\n"
        ...     ".#.\\n"
        ... )
        >>> tree_map_a.get_tree_count_on_slope((1, 1))
        0
        >>> tree_map_a.get_tree_count_on_slope((2, 1))
        1
        >>> tree_map_a.get_tree_count_on_slope((1, 2))
        1
        >>> tree_map_b = TreeMap.from_text(
        ...     "..##.......\\n"
        ...     "#...#...#..\\n"
        ...     ".#....#..#.\\n"
        ...     "..#.#...#.#\\n"
        ...     ".#...##..#.\\n"
        ...     "..#.##.....\\n"
        ...     ".#.#.#....#\\n"
        ...     ".#........#\\n"
        ...     "#.##...#...\\n"
        ...     "#...##....#\\n"
        ...     ".#..#...#.#\\n"
        ... )
        >>> tree_map_b.get_tree_count_on_slope((3, 1))
        7
        >>> tree_map_b.get_tree_count_on_slope((1, 1))
        2
        >>> tree_map_b.get_tree_count_on_slope((5, 1))
        3
        >>> tree_map_b.get_tree_count_on_slope((7, 1))
        4
        >>> tree_map_b.get_tree_count_on_slope((1, 2))
        2
        """
        return self.get_tree_count_on_points(self.get_points_on_slope(slope))

    def get_tree_count_on_points(self, points):
        return sum(
            1
            for x, y in points
            if self.lines[y][x]
        )

    def get_points_on_slope(self, slope):
        """
        >>> tree_map_a = TreeMap.from_text(
        ...     "..#\\n"
        ...     "#..\\n"
        ...     ".#.\\n"
        ... )
        >>> tree_map_a.get_points_on_slope((1, 1))
        [(0, 0), (1, 1), (2, 2)]
        >>> tree_map_a.get_points_on_slope((2, 1))
        [(0, 0), (2, 1), (1, 2)]
        >>> tree_map_a.get_points_on_slope((1, 2))
        [(0, 0), (1, 2)]
        >>> tree_map_b = TreeMap.from_text(
        ...     "..##.......\\n"
        ...     "#...#...#..\\n"
        ...     ".#....#..#.\\n"
        ...     "..#.#...#.#\\n"
        ...     ".#...##..#.\\n"
        ...     "..#.##.....\\n"
        ...     ".#.#.#....#\\n"
        ...     ".#........#\\n"
        ...     "#.##...#...\\n"
        ...     "#...##....#\\n"
        ...     ".#..#...#.#\\n"
        ... )
        >>> tree_map_b.get_points_on_slope((3, 1))
        [(0, 0), (3, 1), (6, 2), (9, 3), (1, 4), (4, 5), (7, 6), (10, 7), (2, 8), (5, 9), (8, 10)]
        """
        delta_x, delta_y = slope
        return [
            ((y // delta_y * delta_x) % self.line_length, y)
            for y in range(0, len(self.lines), delta_y)
        ]


Challenge.main()
challenge = Challenge()