2023 Day 1 Part 2

noahover/aoc23/input/day1_example2.txt

@@ -0,0 +1,7 @@
+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen

noahover/aoc23/lib/day1.ex

@@ -6,12 +6,6 @@ defmodule Day1 do
   def parse_input(input) do
     input
     |> String.split("\n", trim: true)
-    |> Enum.map(fn x ->
-      x
-      |> String.to_charlist()
-      |> Enum.map(fn x -> x - 48 end)
-      |> Enum.filter(fn x -> x >= 0 && x <= 9 end)
-    end)
   end
 
   @doc """
@@ -20,8 +14,21 @@ defmodule Day1 do
   Sum the calibration values which are the first numeral in each line
   as the first digit and the last numeral in each line as the second digit.
   """
-  def sum_calibration_values(digits) do
-    digits
+  def sum_calibration_values(rows) do
+    rows
+    |> Enum.map(fn x -> numerals_from_string(x) end)
+    |> sum_from_numerals()
+  end
+
+  defp numerals_from_string(row) do
+    row
+    |> String.to_charlist()
+    |> Enum.map(fn x -> x - 48 end)
+    |> Enum.filter(fn x -> x >= 0 && x <= 9 end)
+  end
+
+  defp sum_from_numerals(numerals) do
+    numerals
     |> Enum.map(fn x ->
       first_digit = hd(x)
       last_digit = List.last(x)
@@ -30,4 +37,141 @@ defmodule Day1 do
     end)
     |> Enum.sum()
   end
+
+  @doc """
+  Day 1 Part 2
+
+  Sum the calibration values which are the first numeral or spelled out
+  numeral in each line as the first digit and the last numeral or spelled
+  out numeral in each line as the second digit.
+  """
+  def sum_calibration_values_with_words(rows) do
+    rows
+    |> Enum.map(fn x -> words_to_calibration_value(x) end)
+    |> Enum.sum()
+  end
+
+  defp words_to_calibration_value(row) do
+    first_digit = find_first_digit(row)
+    last_digit = find_last_digit(row)
+
+    first_digit * 10 + last_digit
+  end
+
+  defp find_first_digit(row) do
+    valid_digits = [
+      "0",
+      "1",
+      "2",
+      "3",
+      "4",
+      "5",
+      "6",
+      "7",
+      "8",
+      "9",
+      "one",
+      "two",
+      "three",
+      "four",
+      "five",
+      "six",
+      "seven",
+      "eight",
+      "nine"
+    ]
+
+    valid_digits
+    |> Enum.reduce(%{}, fn x, acc ->
+      case :binary.match(row, x) do
+        {index, _length} ->
+          Map.put(acc, x, index)
+
+        _ ->
+          acc
+      end
+    end)
+    |> Map.to_list()
+    |> Enum.sort(fn {_k1, v1}, {_k2, v2} -> v1 < v2 end)
+    |> hd()
+    |> elem(0)
+    |> convert_text_to_number()
+  end
+
+  defp convert_text_to_number(s) do
+    case s do
+      "one" ->
+        1
+
+      "two" ->
+        2
+
+      "three" ->
+        3
+
+      "four" ->
+        4
+
+      "five" ->
+        5
+
+      "six" ->
+        6
+
+      "seven" ->
+        7
+
+      "eight" ->
+        8
+
+      "nine" ->
+        9
+
+      _ ->
+        String.to_integer(s)
+    end
+  end
+
+  defp find_last_digit(row) do
+    valid_digits = [
+      "0",
+      "1",
+      "2",
+      "3",
+      "4",
+      "5",
+      "6",
+      "7",
+      "8",
+      "9",
+      "eno",
+      "owt",
+      "eerht",
+      "ruof",
+      "evif",
+      "xis",
+      "neves",
+      "thgie",
+      "enin"
+    ]
+
+    backwards_row = String.reverse(row)
+
+    valid_digits
+    |> Enum.reduce(%{}, fn x, acc ->
+      case :binary.match(backwards_row, x) do
+        {index, _length} ->
+          Map.put(acc, x, index)
+
+        _ ->
+          acc
+      end
+    end)
+    |> Map.to_list()
+    |> Enum.sort(fn {_k1, v1}, {_k2, v2} -> v1 < v2 end)
+    |> hd()
+    |> elem(0)
+    |> String.reverse()
+    |> convert_text_to_number()
+  end
 end

noahover/aoc23/test/day1_test.exs

@@ -4,9 +4,9 @@ defmodule Day1Test do
 
   import Day1
 
-  test "day 1 part 1 example - sum calibration values" do
+  test "day 1 part 1 example 1 - sum calibration values" do
     answer =
-      File.read!("input/day1_example.txt")
+      File.read!("input/day1_example1.txt")
       |> parse_input()
       |> sum_calibration_values()
 
@@ -21,4 +21,22 @@ defmodule Day1Test do
 
     assert answer == 54450
   end
+
+  test "day 1 part 2 example 2 - sum calibration values with words" do
+    answer =
+      File.read!("input/day1_example2.txt")
+      |> parse_input()
+      |> sum_calibration_values_with_words()
+
+    assert answer == 281
+  end
+
+  test "day 1 part 2 - sum calibration values with words" do
+    answer =
+      File.read!("input/day1.txt")
+      |> parse_input()
+      |> sum_calibration_values_with_words()
+
+    assert answer == 54265
+  end
 end