97 lines
2.5 KiB
Elixir
97 lines
2.5 KiB
Elixir
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defmodule Day7 do
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@example """
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light red bags contain 1 bright white bag, 2 muted yellow bags.
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dark orange bags contain 3 bright white bags, 4 muted yellow bags.
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bright white bags contain 1 shiny gold bag.
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muted yellow bags contain 2 shiny gold bags, 9 faded blue bags.
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shiny gold bags contain 1 dark olive bag, 2 vibrant plum bags.
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dark olive bags contain 3 faded blue bags, 4 dotted black bags.
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vibrant plum bags contain 5 faded blue bags, 6 dotted black bags.
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faded blue bags contain no other bags.
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dotted black bags contain no other bags.
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"""
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@example2 """
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shiny gold bags contain 2 dark red bags.
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dark red bags contain 2 dark orange bags.
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dark orange bags contain 2 dark yellow bags.
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dark yellow bags contain 2 dark green bags.
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dark green bags contain 2 dark blue bags.
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dark blue bags contain 2 dark violet bags.
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dark violet bags contain no other bags.
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"""
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def part1(example \\ false) do
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rules =
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if(example, do: @example, else: File.read!("lib/day7/input.txt"))
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|> parse_rules()
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Map.keys(rules)
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|> Enum.count(fn k ->
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can_contain?(k, "shiny gold", rules)
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end)
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end
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def part2(example \\ false) do
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rules =
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case example do
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false -> File.read!("lib/day7/input.txt")
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1 -> @example
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2 -> @example2
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end
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|> parse_rules()
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# don't count the outermost shiny gold bag itself
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count_contained(rules, "shiny gold") - 1
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end
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def parse_rules(input) do
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input
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|> String.trim()
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|> String.split("\n")
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|> Enum.map(&parse_rule/1)
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|> Map.new()
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end
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def parse_rule(rule) do
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[_, rule_color, rest] = Regex.run(~r/^(\w+ \w+) bags contain (no other bags|.+)\.$/, rule)
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contains =
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case rest do
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"no other bags" ->
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[]
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rest ->
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rest
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|> String.split(",")
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|> Enum.map(fn str ->
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str = String.trim(str)
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[_, qty, color] = Regex.run(~r/^(\d+) (\w+ \w+) bags?$/, str)
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qty = String.to_integer(qty)
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{qty, color}
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end)
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end
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{rule_color, contains}
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end
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def can_contain?(outer, inner, rules) do
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outer_rules = Map.fetch!(rules, outer)
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Enum.any?(outer_rules, fn {_, color} ->
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color == inner || can_contain?(color, inner, rules)
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end)
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end
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def count_contained(rules, color) do
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nested =
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Map.fetch!(rules, color)
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|> Enum.map(fn {qty, contained_color} ->
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qty * count_contained(rules, contained_color)
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end)
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|> Enum.sum()
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1 + nested
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end
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end
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