41 lines
1,004 B
Elixir
41 lines
1,004 B
Elixir
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defmodule Day5Part2 do
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def run do
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File.stream!("input")
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|> Stream.map(&seat_id/1)
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|> Enum.sort()
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|> find_seat()
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|> IO.puts()
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end
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def find_seat([_ | next_seats] = seats) do
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Stream.zip(seats, next_seats)
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|> Enum.find(fn {seat, next} -> next - seat > 1 end)
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|> elem(0)
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|> Kernel.+(1)
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end
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def seat_id(boarding_pass) do
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{row_spec, col_spec} = boarding_pass |> String.trim() |> String.to_charlist() |> Enum.split(7)
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row =
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Enum.reduce(row_spec, {0, 128}, fn
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?F, {front, 2} -> front
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?B, {front, 2} -> front + 1
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?F, {front, count} -> {front, div(count, 2)}
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?B, {front, count} -> {front + div(count, 2), div(count, 2)}
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end)
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col =
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Enum.reduce(col_spec, {0, 8}, fn
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?L, {left, 2} -> left
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?R, {left, 2} -> left + 1
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?L, {left, count} -> {left, div(count, 2)}
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?R, {left, count} -> {left + div(count, 2), div(count, 2)}
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end)
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row * 8 + col
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end
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end
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Day5Part2.run()
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