adventofcode-2021/day06/part2.lua

#!/usr/bin/env luajit
require("utils")
require("deque")

local fishes = deque()
for timer = 0, 9 do
	fishes:append(0)
end

for _, timer in pairs(split(io.open(arg[3]):read("*a"), ",")) do
	fishes:set(tonumber(timer), fishes:get(tonumber(timer)) + 1)
end

for day = 1, 256 do
	local breeding = fishes:popleft() or 0
	fishes:append(0)
	fishes:set(8, (fishes:get(8) or 0) + breeding)
	fishes:set(6, (fishes:get(6) or 0) + breeding)
end

local sum = 0
while fishes.size > 0 do
	sum = sum + (fishes:pop() or 0)
end

print(sum)