adventofcode-2021/day04/part2.lua

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

local f = io.open(arg[3])
local numbers = split(f:read("*l"), ",")
local line = f:read("*l")
local boards = {}
while line ~= nil do
	local board = {}
	for r = 1, 5 do
		line = f:read("*l")
		while line:byte(1) == string.byte(" ", 1) do
			line = line:sub(2)
		end
		board[r] = split(line, " +")
	end
	table.insert(boards, board)
	line = f:read("*l")
end

function finished(board, row, col)
	local j, rowints, colints = 1, 0, 0
	while j <= 5 and (rowints == 0 or colints == 0) do
		if board[row][j] ~= nil then rowints = rowints + 1 end
		if board[j][col] ~= nil then colints = colints + 1 end
		j = j + 1
	end
	return rowints == 0 or colints == 0
end

local i = 1
local complete
while #boards > 0 and i <= #numbers do
	local number = numbers[i]
	local nboards = {}
	for b, board in pairs(boards) do
		complete = board
		local hasfinished = false
		for r, row in pairs(board) do
			for c, col in pairs(row) do
				if col == number then
					row[c] = nil
					if finished(board, r, c) then
						hasfinished = true
					end
				end
			end
		end
		if not hasfinished then
			table.insert(nboards, board)
		end
	end
	boards = nboards

	i = i + 1
end

local sum = 0
for r = 1, 5 do
	for c = 1, 5 do
		sum = sum + (complete[r][c] or 0)
	end
end
print(numbers[i - 1] * sum)