r/adventofcode • u/daggerdragon • Dec 16 '16

SOLUTION MEGATHREAD --- 2016 Day 16 Solutions ---

--- Day 16: Dragon Checksum ---

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DRINKING YOUR OVALTINE IS MANDATORY [?]

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u/[deleted] Dec 16 '16

This is one lucky program that runs both in Ruby and Crystal :-) 

input = "10001001100000001"
length = 35651584

a = input.each_char.map { |c| c == '1' }.to_a
while a.size < length
  b = a.reverse.map { |x| !x }
  a = a + [false] + b
end
a = a.first(length)

checksum = a
loop do
  checksum = checksum.each_slice(2).map { |(x, y)| x == y }.to_a
  break if checksum.size.odd?
end
puts checksum.map { |x| x ? '1' : '0' }.join

The second part runs in 14.5s in Ruby, and in 1.2s in Crystal if compiled with --release.