Advent of Code 2017 Day 2

day2.ex

  defmodule Day2 do
    def parser( input ) do
      String.split( input, "\n" )
      |> Enum.map( fn k ->
        String.split( k, "\t")
        |> Enum.map( &String.to_integer/1 )
      end )
    end
    def start1( input ) do
      input
      |> parser
      |> step1( 0 )
    end
    def step1( [ row | rest ], acc ) do
      step1( rest, acc + step1a( row ) )
    end
    def step1( [], acc ), do: acc

    def step1a( [ e | rest ] ), do: step1a( rest, { e, e } )
    def step1a( [ e | rest ], { low, hi } ) do
      cond do
        e > hi -> step1a( rest, {low, e } )
        e < low -> step1a( rest, { e, hi } )
        true -> step1a( rest, { low, hi } )
      end
    end
    def step1a( [], { low, hi } ), do: hi - low

    def start2( input ) do
      input
      |> parser
      |> step2( 0 )
    end

    def step2( [ row | rest ], acc ), do: step2( rest, acc + step2a( row ) )
    def step2( [], acc ), do: acc

    def step2a( [ a | row ] ) do
      step2b( a, row )
      |> case  do
        nil -> step2a( row )
        val -> val
      end
    end
    def step2a( [] ) do
      IO.puts( "no divisible pair")
      0
    end
    def step2b( a, [ b | row ] ) do
      cond do
        Integer.mod( a, b ) == 0 -> Integer.floor_div( a, b )
        Integer.mod( b, a ) == 0 -> Integer.floor_div( b, a )
        true -> step2b( a, row )
      end
    end
    def step2b( a, [] ) do
      nil
    end
  end