Day 16 Part 1

2020/day16/day16.ex

@@ -0,0 +1,85 @@
+defmodule Day16 do
+  defp read_input do
+    Path.expand('input', Path.dirname(__ENV__.file))
+    |> File.read!()
+  end
+
+  defp test_input do
+    """
+    class: 1-3 or 5-7
+    row: 6-11 or 33-44
+    seat: 13-40 or 45-50
+
+    your ticket:
+    7,1,14
+
+    nearby tickets:
+    7,3,47
+    40,4,50
+    55,2,20
+    38,6,12
+    """
+  end
+
+  defp parse_input(text) do
+    [fields, mine, nearby] = String.split(text, "\n\n", trim: true)
+    [_, my_ticket] = String.split(mine, "\n", trim: true)
+    [_ | nearby_tickets] = String.split(nearby, "\n", trim: true)
+
+    {
+      parse_fields(fields),
+      parse_ticket(my_ticket),
+      Enum.map(nearby_tickets, &parse_ticket/1)
+    }
+  end
+
+  @field_pattern ~r/^(?<name>.*): (?<range1_lo>\d+)-(?<range1_hi>\d+) or (?<range2_lo>\d+)-(?<range2_hi>\d+)$/
+
+  defp parse_fields(text) do
+    String.split(text, "\n")
+    |> Enum.map(fn line ->
+      %{
+        "name" => name,
+        "range1_lo" => range1_lo,
+        "range1_hi" => range1_hi,
+        "range2_lo" => range2_lo,
+        "range2_hi" => range2_hi
+      } = Regex.named_captures(@field_pattern, line)
+
+      r1_lo = String.to_integer(range1_lo)
+      r1_hi = String.to_integer(range1_hi)
+      r2_lo = String.to_integer(range2_lo)
+      r2_hi = String.to_integer(range2_hi)
+      {name, r1_lo..r1_hi, r2_lo..r2_hi}
+    end)
+  end
+
+  defp parse_ticket(line) do
+    String.split(line, ",", trim: true)
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  defp validate(fields, ticket) do
+    Enum.reject(ticket, fn value ->
+      Enum.any?(fields, &can_match?(&1, value))
+    end)
+    |> Enum.sum()
+  end
+
+  defp can_match?({_name, r1, r2}, value) do
+    in_range?(r1, value) or in_range?(r2, value)
+  end
+
+  defp in_range?(lo..hi, val) do
+    lo <= val and val <= hi
+  end
+
+  def part1 do
+    {fields, _mine, nearby} = read_input() |> parse_input()
+
+    Enum.map(nearby, &validate(fields, &1))
+    |> Enum.sum()
+  end
+end
+
+Day16.part1() |> IO.inspect()