Advent of Code 2024 - Day 03

Solutions

input = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"
pattern = ~r/mul\(\d+,\d+\)/

matches = Regex.scan(pattern, input) |> List.flatten()
IO.inspect(matches)

input = "mul(2,4)"

# Use pattern matching to extract numbers
result =
  case Regex.run(~r/mul\((\d+),(\d+)\)/, input) do
    [_, num1, num2] ->
      # Convert strings to integers and multiply
      String.to_integer(num1) * String.to_integer(num2)

    _ ->
      "Invalid input"
  end

IO.puts("Result: #{result}")

defmodule Day03 do
  def parse(string) do
    pattern = ~r/mul\(\d+,\d+\)/
    Regex.scan(pattern, string) |> List.flatten()
  end

  def multiply(string) do
      case Regex.run(~r/mul\((\d+),(\d+)\)/, string) do
    [_, num1, num2] ->
      String.to_integer(num1) * String.to_integer(num2)
    _ ->
      "Invalid input"
  end
    
    
  end


  def multiply_all(list) do
    list  
    |> Enum.map(&multiply/1)
    |> Enum.sum()  
  end

  def task1(string) do
    string
    |> parse()
    |> multiply_all()
  end
  
end

input = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"
Day03.task1(input)

input = File.read!("/data/files/input.txt")
Day03.task1(input)

input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))"
pattern = ~r/mul\(\d+,\d+\)|do\(\)|don't\(\)/

matches = Regex.scan(pattern, input) |> List.flatten()
IO.inspect(matches)

defmodule FilterMul do
  def filter_mul_operations(list) do
    list
    |> Enum.reduce({[], true}, fn
      "do()", {acc, _} -> {acc, true}  # Start adding mul items after "do()"
      "don't()", {acc, _} -> {acc, false}  # Stop adding mul items after "don't()"
      mul, {acc, true} -> 
        if String.starts_with?(mul, "mul") do
          {[mul | acc], true}  # Collect mul items during "do()" phase
        else
          {acc, true}  # Ignore non-mul items during "do()" phase
        end
      _other, acc -> acc  # Keep current state for other items
    end)
    |> elem(0)
    |> Enum.reverse()  # Reverse the list to maintain correct order
  end
end

# Example usage:
lst = ["mul(2,4)", "don't()", "mul(5,5)", "mul(11,8)", "do()", "mul(8,5)", "mul(87,5)", "mul(87,5)", "don't()", "mul(87,50)"]
IO.inspect(FilterMul.filter_mul_operations(lst))

defmodule Day03b do
  def parse(string) do
    pattern = ~r/mul\(\d+,\d+\)|do\(\)|don't\(\)/
    Regex.scan(pattern, string) |> List.flatten()
  end

  def multiply(string) do
      case Regex.run(~r/mul\((\d+),(\d+)\)/, string) do
    [_, num1, num2] ->
      String.to_integer(num1) * String.to_integer(num2)
    _ ->
      "Invalid input"
  end
    
  end
  
  def remove_donts(list) do 

    list
    |> Enum.reduce({[], true}, fn
      "do()", {acc, _} -> {acc, true}  # Start adding mul items after "do()"
      "don't()", {acc, _} -> {acc, false}  # Stop adding mul items after "don't()"
      mul, {acc, true} -> 
          {[mul | acc], true}  # Collect mul items during "do()" phase
      _other, acc -> acc  # Keep current state for other items
    end)
    |> elem(0)
 
  end

  
  def multiply_all(list) do
    list  
    |> Enum.map(&multiply/1)
    |> Enum.sum()  
  end

  def task2(string) do
    string
    |> parse()
    |> remove_donts()
    |> multiply_all()
  end
  
end

input = File.read!("/data/files/input.txt")
Day03b.task2(input)