defmodule Population do
    def count_people(people) do
        people
            |> Enum.reduce(%{}, fn (%{ birth: birth, death: death }, acc) ->
                acc
                    |> Map.update(birth, 1, &(&1 + 1))
                    |> Map.update(death, -1, &(&1 - 1))
            end)
            |> IO.inspect
            |> Enum.scan({0, 0}, fn({ year, population }, { _, population_acc }) ->
                IO.puts year
                { year, population + population_acc }
            end)
            |> Enum.max_by(fn({_, year}) -> year end)
    end
end
 
IO.puts "There are 32 unique years in this list. Notice that they're traversed in order"
0..31
    |> Enum.map(&(%{ birth: &1, death: 31 - &1 }))
    |> Population.count_people
    |> IO.inspect
 
IO.puts "There are 33 in this one...hmmm..."
0..32
    |> Enum.map(&(%{ birth: &1, death: 32 - &1 }))
    |> Population.count_people
    |> IO.inspect
 

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