64 lines
1.3 KiB
Elixir
64 lines
1.3 KiB
Elixir
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defmodule Day3 do
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@example """
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..##.......
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#...#...#..
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.#....#..#.
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..#.#...#.#
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.#...##..#.
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..#.##.....
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.#.#.#....#
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.#........#
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#.##...#...
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#...##....#
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.#..#...#.#
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"""
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def part1(example \\ false) do
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count_trees(example, {3, 1})
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end
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def part2(example \\ false) do
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one_one = count_trees(example, {1, 1})
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three_one = count_trees(example, {3, 1})
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five_one = count_trees(example, {5, 1})
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seven_one = count_trees(example, {7, 1})
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one_two = count_trees(example, {1, 2})
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one_one * three_one * five_one * seven_one * one_two
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end
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def count_trees(example, slope) do
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example
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|> parse_input()
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|> count_trees_for_slope(slope)
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end
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def parse_input(example) do
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if(example, do: @example, else: File.read!("lib/day3/input.txt"))
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(fn line ->
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line
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|> String.codepoints()
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|> Enum.map(fn
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"#" -> 1
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_ -> 0
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end)
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|> Stream.cycle()
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end)
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end
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def count_trees_for_slope(lines, slope) do
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do_count(lines, slope, 0, 0)
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end
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def do_count([current | rest], {dx, dy} = slope, x, trees) do
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rest = Enum.drop(rest, dy - 1)
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do_count(rest, slope, x + dx, trees + Enum.at(current, x))
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end
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def do_count([], _, _, trees) do
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trees
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end
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end
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