Day 4 Parts 1 and 2

README.md

@@ -2,7 +2,7 @@
 
 My (attempted) solutions to [Advent of Code 2020](https://adventofcode.com/2020) in Elixir.
 
-<img width="973" alt="image" src="https://user-images.githubusercontent.com/498229/100967992-db331000-3573-11eb-8a48-aa73d01f1a53.png">
+<img width="970" alt="image" src="https://user-images.githubusercontent.com/498229/101128533-397af400-3643-11eb-8555-c78113d57aa5.png">
 
 ## Strategy
 

day4/README

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+Day 4 Notes
+
++--------+
+| Part 1 |
++--------+
+
+$ elixir day4part1.exs
+210
+
+Thoughts:
+
+Parse each passport into a list of key-value pairs, and extract the keys.
+Not sure if there will be extra keys, so store required keys in a Mapset, which means I can use
+MapSet.subset to make sure all the required keys are present.
+Embedded enums are kind of ugly.
+Nice usage of Enum.into, IMO 🍠.
+
++--------+
+| Part 2 |
++--------+
+
+$ elixir day4part2.exs
+131
+
+Thoughts:
+
+Need the values too now, so refactor a bit to preserve them, storing each passport at a map.
+Can still use part 1 logic to filter out passports that have missing keys.
+ - just pull out the keys and convert to a MapSet as before.
+Delete the cid key if present, since needs to be ignored.
+
+Validation code:
+Mostly just implementing the spec.
+Use regex for fiddly requirements.
+hgt was a bit annoying, really wanted to fail-fast if the regex failed to match the units,
+maybe will come back to that and think of a nicer way later.
+For valid?: Is there a nicer way to call a bunch of functions with the same argument and
+aggregate their results? 🤔
+
+
++------------------+
+| Overall Thoughts |
++------------------+
+
+Starting to take me longer now, about an hour for this one.
+Ended up not using Enum.reduce here, but every time I do use it I forget the order of the
+acc/item pair in the reducer function... 😩

day4/day4part1.exs

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+defmodule Day4Part1 do
+  @required MapSet.new(["byr", "ecl", "eyr", "hcl", "hgt", "iyr", "pid"])
+
+  def run do
+    File.read!("input")
+    |> String.trim()
+    |> String.split("\n\n")
+    |> Enum.map(fn passport ->
+      passport
+      |> String.split([" ", "\n"])
+      |> Enum.map(&String.split(&1, ":"))
+      |> Enum.into(MapSet.new(), fn [k, _] -> k end)
+    end)
+    |> Enum.count(&MapSet.subset?(@required, &1))
+    |> IO.puts()
+  end
+end
+
+Day4Part1.run()

day4/day4part2.exs

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+defmodule Day4Part2 do
+  @required MapSet.new(["byr", "ecl", "eyr", "hcl", "hgt", "iyr", "pid"])
+
+  def run do
+    File.read!("input")
+    |> String.trim()
+    |> String.split("\n\n")
+    |> Enum.map(fn passport ->
+      passport
+      |> String.split([" ", "\n"])
+      |> Enum.map(&String.split(&1, ":"))
+      |> Map.new(fn [k, v] -> {k, v} end)
+    end)
+    |> Enum.map(&Map.delete(&1, "cid"))
+    |> Enum.filter(&MapSet.subset?(@required, &1 |> Map.keys() |> MapSet.new()))
+    |> Enum.count(&valid?/1)
+    |> IO.puts()
+  end
+
+  def valid?(passport) do
+    byr?(passport) && iyr?(passport) && eyr?(passport) && hgt?(passport) && hcl?(passport) &&
+      ecl?(passport) && pid?(passport)
+  end
+
+  def byr?(%{"byr" => byr}) do
+    date = String.to_integer(byr)
+    1920 <= date && date <= 2002
+  end
+
+  def iyr?(%{"iyr" => iyr}) do
+    date = String.to_integer(iyr)
+    2010 <= date && date <= 2020
+  end
+
+  def eyr?(%{"eyr" => eyr}) do
+    date = String.to_integer(eyr)
+    2020 <= date && date <= 2030
+  end
+
+  def hgt?(%{"hgt" => hgt}) do
+    {hgt, unit} =
+      case Regex.run(~r/\A(\d+)([^\d]+)\z/, hgt, capture: :all_but_first) do
+        [hgt, unit] -> {String.to_integer(hgt), unit}
+        nil -> {0, nil}
+      end
+
+    case unit do
+      "cm" -> 150 <= hgt && hgt <= 193
+      "in" -> 59 <= hgt && hgt <= 76
+      nil -> false
+    end
+  end
+
+  def hcl?(%{"hcl" => hcl}) do
+    Regex.match?(~r/\A#[0-9a-f]{6}\z/, hcl)
+  end
+
+  def ecl?(%{"ecl" => ecl}) do
+    ecl in ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]
+  end
+
+  def pid?(%{"pid" => pid}) do
+    Regex.match?(~r/\A\d{9}\z/, pid)
+  end
+end
+
+Day4Part2.run()