WITH MUTUALLY RECURSIVE
lines(line TEXT) AS ( SELECT regexp_split_to_table(input, '\n') FROM input ),
links(name TEXT, link TEXT) AS (
SELECT
substring(regexp_split_to_array(line, ' ')[1], 2),
trim(',' FROM regexp_split_to_array(line, ' ')[x])
FROM
lines, generate_series(3, array_length(regexp_split_to_array(line, ' '), 1)) x
),
-- One special line has op 'b' and name 'roadcaster'.
types(op TEXT, name TEXT) AS (
SELECT
substring(regexp_split_to_array(line, ' ')[1], 1, 1),
substring(regexp_split_to_array(line, ' ')[1], 2)
FROM
lines
),
-- Part one: simulate 1000 steps of 'broadcaster' being activated with a low pulse.
-- tally up total low and high pulses, and then multiply.
-- The state carried across steps are the last-transmitted pulses of each operator.
-- This should also tell us the final state of the `%` operators.
-- We'll also need the totals of low and high pulses, so that we can add them up.
seed(press INT, counter INT) AS (
SELECT 1, 1
UNION
SELECT press, counter - 1
FROM seed
WHERE counter > 0
UNION
SELECT press + 1, 20
FROM seed
WHERE counter = 0
AND press < 4100
),
-- Emitted pulses after various button presses, in various rounds of resolution.
pulses(name TEXT, press INT, round INT, pulse TEXT) AS (
-- One thousand button presses, each followed by rounds of resolution.
SELECT 'roadcaster', press, 1, 'lo' FROM seed WHERE counter = 0
UNION ALL SELECT * FROM flip
UNION ALL SELECT * FROM conj
),
-- Counters; every 'lo' input pulse flips and emits the state.
flip(name TEXT, press INT, round INT, pulse TEXT) AS (
-- Each `signal` needs to behave as if all "prior" signals have been processed, ordered by (press, round, source).
SELECT
name,
press,
round + 1,
-- Look for the most recently emitted signal, and we'll produce the opposite of that one.
CASE WHEN (
SELECT COUNT(*)
FROM signal s1
WHERE s1.target = types.name
AND s1.pulse = 'lo'
AND ((s1.press < signal.press) OR
(s1.press = signal.press AND s1.round < signal.round) OR
(s1.press = signal.press AND s1.round = signal.round AND s1.source < signal.source))
) % 2 = 0
THEN 'hi'
ELSE 'lo'
END
FROM signal, types
WHERE signal.target = types.name
AND types.op = '%'
AND signal.pulse = 'lo'
),
-- NAND gates; every input pulse evokes the NAND of most recent inputs.
conj(name TEXT, press INT, round INT, pulse TEXT) AS (
SELECT
name,
press,
round + 1,
-- Look for the most recently received signals from each input,
-- including this one, and iff all 'hi' then 'lo'.
CASE WHEN (
(SELECT COUNT(*) FROM links WHERE link = types.name)
=
(SELECT COUNT(*) FROM (
SELECT DISTINCT ON (source) source, pulse
FROM signal s1
WHERE s1.target = types.name
AND ((s1.press < signal.press) OR
(s1.press = signal.press AND s1.round < signal.round) OR
(s1.press = signal.press AND s1.round = signal.round AND s1.source <= signal.source))
OPTIONS (DISTINCT ON INPUT GROUP SIZE = 1000)
ORDER BY source, press DESC, round DESC
)
WHERE pulse = 'hi'))
THEN 'lo'
ELSE 'hi'
END
FROM signal, types
WHERE signal.target = types.name
AND types.op = '&'
),
-- A record of a pulse into an operator, from another operator.
-- We track the source so that '&' operators can make any sense.
signal(source TEXT, target TEXT, press INT, round INT, pulse TEXT) AS (
SELECT pulses.name, links.link, pulses.press, pulses.round, pulses.pulse
FROM pulses, links
WHERE pulses.name = links.name
AND pulses.round > 0
),
part1(pulse TEXT, count BIGINT) AS (
SELECT pulse, count(*) FROM signal GROUP BY pulse
),
potato(x INT) AS (SELECT 1)
SELECT * FROM signal WHERE target = 'cn' AND pulse = 'hi';Day 20 was brought to you by: @frankmcsherry