Day 5

lib/day5/day5.ex

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+defmodule Day5 do
+  
+  @doc """
+  Compares two codepoints for opposite case.
+
+  ## Examples
+
+      iex> Day5.react('dabAcCaCBAcCcaDA')
+      'dabCBAcaDA'
+
+  """
+  def react(chars) do
+    chars
+    |> Enum.reduce('', fn
+      c, [prev | rest] = s ->
+        if oppCase(c, prev) do
+          rest
+        else
+          [c | s]
+        end
+      c, [] ->
+        [c]
+    end)
+    |> Enum.reverse()
+    |> case do
+      ^chars -> chars
+      remaining -> react(remaining)
+    end
+  end
+
+  @doc """
+  Compares two codepoints for opposite case.
+
+  ## Examples
+
+      iex> Day5.oppCase(?a, ?A)
+      true
+      iex> Day5.oppCase(?A, ?a)
+      true
+      iex> Day5.oppCase(?A, ?A)
+      false
+      iex> Day5.oppCase(?B, ?A)
+      false
+
+  """
+  def oppCase(c1, c2) do
+    s1 = <<c1::utf8>>
+    s2 = <<c2::utf8>>
+    lower1 = String.downcase(s1)
+    upper1 = String.upcase(s1)
+    lower2 = String.downcase(s2)
+
+    cond do
+      lower1 != lower2 -> false
+      s1 == lower1 && s1 == s2 -> false
+      s1 == upper1 && s1 == s2 -> false
+      true -> true
+    end
+  end
+
+  @doc """
+  Compares two codepoints for opposite case.
+
+  ## Examples
+
+      iex> Day5.min_length("dabAcCaCBAcCcaDA")
+      4
+
+  """
+  def min_length(input) do
+    input
+    |> String.downcase()
+    |> String.to_charlist()
+    |> Enum.uniq()
+    |> Enum.map(fn c ->
+      s = <<c::utf8>>
+      str = String.replace(input, s, "")
+      str = String.replace(str, String.upcase(s), "")
+      input
+      |> String.replace(s, "")
+      |> String.replace(String.upcase(s), "")
+      |> String.to_charlist()
+      |> react()
+    end)
+    |> Enum.min_by(&length/1)
+    |> length()
+  end
+
+  def parse_input() do
+    File.read!("lib/day5/input.txt")    
+  end
+
+  def part1() do
+    parse_input()
+    |> String.to_charlist()
+    |> react()
+    |> length()
+  end
+
+  def part2() do
+    parse_input()
+    |> min_length()
+  end
+
+end

test/day5/day5_test.exs

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+defmodule Day5Test do
+  use ExUnit.Case
+  doctest Day5
+end