defmodule Day4 do defmodule Timestamp do defstruct [:year, :month, :day, :hour, :minute] def create(y, m, d, h, min) do %Timestamp{ year: y |> String.to_integer(), month: m |> String.to_integer(), day: d |> String.to_integer(), hour: h |> String.to_integer(), minute: min |> String.to_integer } end def range(first, second) do first.minute..second.minute end end def parse_event(line) do res = Regex.run(~r/\[(\d+)-(\d+)-(\d+) (\d+):(\d+)\] (.+)/, line) [_line, y, m, d, h, min, event | _tail] = res { Timestamp.create(y, m, d, h, min), event } end def parse_events(lines) do lines |> Enum.map(&parse_event/1) end def sort_events(events) do events |> Enum.sort_by(fn {ts, _} -> {ts.year, ts.month, ts.day, ts.hour, ts.minute} end) end def parse_guard({_, msg}) do case Regex.run(~r/Guard #(\d+) begins shift/, msg) do [_event, id | _tail] -> id _ -> nil end end def get_sleep_times(events) do chunk_fun = fn event, acc -> case parse_guard(event) do nil -> {:cont, [event | acc]} _id -> {:cont, Enum.reverse(acc), [event]} end end after_fun = fn [] -> {:cont, []} acc -> {:cont, Enum.reverse(acc), acc} end events |> Enum.chunk_while([], chunk_fun, after_fun) |> Enum.reject(fn [] -> true _ -> false end) |> Enum.reduce(%{}, fn [begin_shift | events], acc -> guard_id = parse_guard(begin_shift) ranges = events |> Enum.chunk_every(2) |> Enum.map(fn [{sleep, _}, {wake, _} | []] -> Timestamp.range(sleep, wake) end) Map.update(acc, guard_id, ranges, &(&1 ++ ranges)) end) |> Enum.reject(fn {_id, []} -> true _ -> false end) end def get_max_sleep_time(guards) do guards |> Enum.map(fn {id, times} -> total = times |> Enum.map(fn a..b -> b - a end) |> Enum.sum() {minute, _count} = times |> Enum.flat_map(&Enum.to_list/1) |> Enum.reduce(%{}, fn minute, acc -> Map.update(acc, minute, 1, &(&1 + 1)) end) |> Enum.max_by(fn {_minute, count} -> count end) {id, total, minute} end) |> Enum.max_by(fn {_id, total, _minute} -> total end) end def range_containing(ranges) do first = Enum.reduce(ranges, Enum.at(ranges, 0).first, fn first.._, acc -> min(first, acc) end) last = Enum.reduce(ranges, Enum.at(ranges, 0).last, fn _..last, acc -> max(last, acc) end) first..last end def get_most_frequent_sleep_time(guards) do guards |> Enum.map(fn {id, times} -> {minute, count} = range_containing(times) |> Enum.map(fn minute -> {minute, Enum.count(times, fn range -> minute in range end)} end) |> Enum.max_by(fn {_minute, count} -> count end) {id, minute, count} end) |> Enum.max_by(fn {_id, _minute, count} -> count end) end def parse_input() do File.read!("lib/day4/input.txt") |> String.split("\n", trim: true) end def part1() do {id, _total, minute} = parse_input() |> parse_events() |> sort_events() |> get_sleep_times() |> get_max_sleep_time() String.to_integer(id) * minute end def part2() do {id, minute, _count} = parse_input() |> parse_events() |> sort_events() |> get_sleep_times() |> get_most_frequent_sleep_time() String.to_integer(id) * minute end end