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| 1 | +defmodule AdventOfCode.Y2023.Day20 do |
| 2 | + @moduledoc """ |
| 3 | + --- Day 20: Pulse Propagation --- |
| 4 | + Problem Link: https://adventofcode.com/2023/day/20 |
| 5 | + Difficulty: h |
| 6 | + Tags: simulation logic-circuit graph cycles lcm |
| 7 | + """ |
| 8 | + alias AdventOfCode.Helpers.{InputReader, Transformers} |
| 9 | + |
| 10 | + def input, do: InputReader.read_from_file(2023, 20) |
| 11 | + |
| 12 | + def run(input \\ input()) do |
| 13 | + {modules, graph} = parse_modules(input) |
| 14 | + |
| 15 | + {run_1(modules, graph), run_2(modules, graph)} |
| 16 | + end |
| 17 | + |
| 18 | + defp run_1(modules, graph) do |
| 19 | + state = init_state(modules, graph) |
| 20 | + |
| 21 | + {_final_state, {lows, highs}} = |
| 22 | + Enum.reduce(1..1000, {state, {0, 0}}, fn _, {curr_state, {l, h}} -> |
| 23 | + {next_state, {new_l, new_h}} = |
| 24 | + send_pulse(curr_state, modules, {"button", "broadcaster", :low}) |
| 25 | + |
| 26 | + {next_state, {l + new_l, h + new_h}} |
| 27 | + end) |
| 28 | + |
| 29 | + lows * highs |
| 30 | + end |
| 31 | + |
| 32 | + defp run_2(modules, graph) do |
| 33 | + hb = graph |> Map.get("rx") |> hd() |
| 34 | + ancestors = Map.get(graph, hb, []) |
| 35 | + |
| 36 | + state = init_state(modules, graph) |
| 37 | + |
| 38 | + periods = |
| 39 | + Enum.reduce_while(Stream.iterate(1, &(&1 + 1)), {state, %{}}, fn press, |
| 40 | + {curr_state, found} -> |
| 41 | + {next_state, high_events} = |
| 42 | + send_pulse_with_tracking(curr_state, modules, {"button", "broadcaster", :low}) |
| 43 | + |
| 44 | + new_found = |
| 45 | + Enum.reduce(high_events, found, fn {from, _to, pulse}, acc -> |
| 46 | + if pulse == :high and from in ancestors and !Map.has_key?(acc, from) do |
| 47 | + Map.put(acc, from, press) |
| 48 | + else |
| 49 | + acc |
| 50 | + end |
| 51 | + end) |
| 52 | + |
| 53 | + if map_size(new_found) == length(ancestors) do |
| 54 | + {:halt, new_found} |
| 55 | + else |
| 56 | + {:cont, {next_state, new_found}} |
| 57 | + end |
| 58 | + end) |
| 59 | + |
| 60 | + periods |> Map.values() |> Enum.reduce(1, &lcm/2) |
| 61 | + end |
| 62 | + |
| 63 | + defp send_pulse(state, modules, initial_pulse) do |
| 64 | + q = :queue.from_list([initial_pulse]) |
| 65 | + process_pulses(q, state, modules, {0, 0}) |
| 66 | + end |
| 67 | + |
| 68 | + defp process_pulses(q, state, modules, {l, h}) do |
| 69 | + case :queue.out(q) do |
| 70 | + {:empty, _} -> |
| 71 | + {state, {l, h}} |
| 72 | + |
| 73 | + {{:value, {from, to, pulse}}, rest} -> |
| 74 | + {new_l, new_h} = if pulse == :low, do: {l + 1, h}, else: {l, h + 1} |
| 75 | + |
| 76 | + case Map.get(modules, to) do |
| 77 | + nil -> |
| 78 | + process_pulses(rest, state, modules, {new_l, new_h}) |
| 79 | + |
| 80 | + %{type: :broadcaster, dests: dests} -> |
| 81 | + new_pulses = Enum.map(dests, fn d -> {to, d, pulse} end) |
| 82 | + process_pulses(enqueue_list(rest, new_pulses), state, modules, {new_l, new_h}) |
| 83 | + |
| 84 | + %{type: :flip_flop, dests: dests} -> |
| 85 | + if pulse == :high do |
| 86 | + process_pulses(rest, state, modules, {new_l, new_h}) |
| 87 | + else |
| 88 | + curr_on = Map.get(state, to) |
| 89 | + new_state = Map.put(state, to, !curr_on) |
| 90 | + new_pulse = if curr_on, do: :low, else: :high |
| 91 | + new_pulses = Enum.map(dests, fn d -> {to, d, new_pulse} end) |
| 92 | + process_pulses(enqueue_list(rest, new_pulses), new_state, modules, {new_l, new_h}) |
| 93 | + end |
| 94 | + |
| 95 | + %{type: :conjunction, dests: dests} -> |
| 96 | + conj_state = Map.get(state, to) |> Map.put(from, pulse) |
| 97 | + new_state = Map.put(state, to, conj_state) |
| 98 | + |
| 99 | + output_pulse = |
| 100 | + if Enum.all?(conj_state, fn {_, p} -> p == :high end), do: :low, else: :high |
| 101 | + |
| 102 | + new_pulses = Enum.map(dests, fn d -> {to, d, output_pulse} end) |
| 103 | + process_pulses(enqueue_list(rest, new_pulses), new_state, modules, {new_l, new_h}) |
| 104 | + end |
| 105 | + end |
| 106 | + end |
| 107 | + |
| 108 | + defp send_pulse_with_tracking(state, modules, initial_pulse) do |
| 109 | + q = :queue.from_list([initial_pulse]) |
| 110 | + process_pulses_tracking(q, state, modules, []) |
| 111 | + end |
| 112 | + |
| 113 | + defp process_pulses_tracking(q, state, modules, events) do |
| 114 | + case :queue.out(q) do |
| 115 | + {:empty, _} -> |
| 116 | + {state, Enum.reverse(events)} |
| 117 | + |
| 118 | + {{:value, {from, to, pulse}}, rest} -> |
| 119 | + new_events = [{from, to, pulse} | events] |
| 120 | + |
| 121 | + case Map.get(modules, to) do |
| 122 | + nil -> |
| 123 | + process_pulses_tracking(rest, state, modules, new_events) |
| 124 | + |
| 125 | + %{type: :broadcaster, dests: dests} -> |
| 126 | + new_pulses = Enum.map(dests, fn d -> {to, d, pulse} end) |
| 127 | + process_pulses_tracking(enqueue_list(rest, new_pulses), state, modules, new_events) |
| 128 | + |
| 129 | + %{type: :flip_flop, dests: dests} -> |
| 130 | + if pulse == :high do |
| 131 | + process_pulses_tracking(rest, state, modules, new_events) |
| 132 | + else |
| 133 | + curr_on = Map.get(state, to) |
| 134 | + new_state = Map.put(state, to, !curr_on) |
| 135 | + new_pulse = if curr_on, do: :low, else: :high |
| 136 | + new_pulses = Enum.map(dests, fn d -> {to, d, new_pulse} end) |
| 137 | + |
| 138 | + process_pulses_tracking( |
| 139 | + enqueue_list(rest, new_pulses), |
| 140 | + new_state, |
| 141 | + modules, |
| 142 | + new_events |
| 143 | + ) |
| 144 | + end |
| 145 | + |
| 146 | + %{type: :conjunction, dests: dests} -> |
| 147 | + conj_state = Map.get(state, to) |> Map.put(from, pulse) |
| 148 | + new_state = Map.put(state, to, conj_state) |
| 149 | + |
| 150 | + output_pulse = |
| 151 | + if Enum.all?(conj_state, fn {_, p} -> p == :high end), do: :low, else: :high |
| 152 | + |
| 153 | + new_pulses = Enum.map(dests, fn d -> {to, d, output_pulse} end) |
| 154 | + |
| 155 | + process_pulses_tracking( |
| 156 | + enqueue_list(rest, new_pulses), |
| 157 | + new_state, |
| 158 | + modules, |
| 159 | + new_events |
| 160 | + ) |
| 161 | + end |
| 162 | + end |
| 163 | + end |
| 164 | + |
| 165 | + defp enqueue_list(q, list) do |
| 166 | + Enum.reduce(list, q, fn item, acc -> :queue.in(item, acc) end) |
| 167 | + end |
| 168 | + |
| 169 | + defp init_state(modules, graph) do |
| 170 | + Enum.reduce(modules, %{}, fn |
| 171 | + {name, %{type: :flip_flop}}, acc -> |
| 172 | + Map.put(acc, name, false) |
| 173 | + |
| 174 | + {name, %{type: :conjunction}}, acc -> |
| 175 | + inputs = Map.get(graph, name, []) |
| 176 | + Map.put(acc, name, Map.new(inputs, &{&1, :low})) |
| 177 | + |
| 178 | + _, acc -> |
| 179 | + acc |
| 180 | + end) |
| 181 | + end |
| 182 | + |
| 183 | + defp parse_modules(data) do |
| 184 | + modules = |
| 185 | + data |
| 186 | + |> Transformers.lines() |
| 187 | + |> Enum.map(fn line -> |
| 188 | + [src_raw, dests_raw] = String.split(line, " -> ") |
| 189 | + dests = String.split(dests_raw, ", ") |
| 190 | + |
| 191 | + {name, type} = |
| 192 | + cond do |
| 193 | + String.starts_with?(src_raw, "%") -> |
| 194 | + {String.replace_prefix(src_raw, "%", ""), :flip_flop} |
| 195 | + |
| 196 | + String.starts_with?(src_raw, "&") -> |
| 197 | + {String.replace_prefix(src_raw, "&", ""), :conjunction} |
| 198 | + |
| 199 | + src_raw == "broadcaster" -> |
| 200 | + {"broadcaster", :broadcaster} |
| 201 | + end |
| 202 | + |
| 203 | + {name, %{type: type, dests: dests}} |
| 204 | + end) |
| 205 | + |> Map.new() |
| 206 | + |
| 207 | + edges = for {name, %{dests: ds}} <- modules, d <- ds, do: {d, name} |
| 208 | + graph = Enum.group_by(edges, &elem(&1, 0), &elem(&1, 1)) |
| 209 | + |
| 210 | + {modules, graph} |
| 211 | + end |
| 212 | + |
| 213 | + defp gcd(a, 0), do: a |
| 214 | + defp gcd(a, b), do: gcd(b, rem(a, b)) |
| 215 | + defp lcm(a, b), do: div(abs(a * b), gcd(a, b)) |
| 216 | + |
| 217 | + def parse(data \\ input()) do |
| 218 | + data |> Transformers.lines() |
| 219 | + end |
| 220 | +end |
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