Advent of Code, 2015, Lua

D10P1.lua

-- NOTE: Input as a table sequence
local str = {}

local getOutput = function(str)
	local out = {}
	local curr, next = -1, -1
	local counter = 1

	for i = 1, #str do
		curr = str[i]
		next = str[i + 1]

		if curr == next then
			counter = counter + 1
		else
			table.insert(out, counter)
			table.insert(out, curr)
			counter = 1
		end
	end

	return out
end

local out = getOutput(str)
for i = 1, 39 do
	out = getOutput(out)
end

io.write(('Length: %d\n'):format(#out))

D10P2.lua

-- NOTE: Input as a table sequence
local str = {}

local getOutput = function(str)
	local out = {}
	local curr, next = -1, -1
	local counter = 1

	for i = 1, #str do
		curr = str[i]
		next = str[i + 1]

		if curr == next then
			counter = counter + 1
		else
			table.insert(out, counter)
			table.insert(out, curr)
			counter = 1
		end
	end

	return out
end

local out = getOutput(str)
for i = 1, 49 do
	out = getOutput(out)
end

io.write(('Length: %d\n'):format(#out))

D11P1.lua

local str = '__your_input__'

local isValid = function(password)
	-- Contains i, o, or l
	if password:match('[iol]') then
		return false
	end

	-- Doubles
	if not str:match('(.)%1.*(.)%2') then
		return false
	end

	-- No three char increasing sequence
	local found = false
	for i = 1, #str - 3 do
		ch1 = password:sub(i, i):byte()
		ch2 = password:sub(i + 1, i + 1):byte()
		ch3 = password:sub(i + 2, i + 2):byte()

		if ch1 == ch2 - 1 and ch2 == ch3 - 1 then
			found = true
			break
		end
	end

	return found
end

local replace = function(str, pos, new)
	return ('%s%s%s'):format(str:sub(1, pos - 1), new, str:sub(pos + 1))
end

local getNext = function(str)
	local i = #str
	while i > 1 and str:sub(i, i) == 'z' do
		str = replace(str, i, 'a')
		i = i - 1
	end

	str = replace(str, i, string.char(str:sub(i, i):byte() + 1))
	return str
end

repeat
	str = getNext(str)
until isValid(str)

io.write(('New password: %s\n'):format(str))

D11P2.lua

-- NOTE: It's exactly the same as D11P1.lua
local str = '__your_input__'

local isValid = function(password)
	-- Contains i, o, or l
	if password:match('[iol]') then
		return false
	end

	-- Doubles
	if not str:match('(.)%1.*(.)%2') then
		return false
	end

	-- No three char increasing sequence
	local found = false
	for i = 1, #str - 3 do
		ch1 = password:sub(i, i):byte()
		ch2 = password:sub(i + 1, i + 1):byte()
		ch3 = password:sub(i + 2, i + 2):byte()

		if ch1 == ch2 - 1 and ch2 == ch3 - 1 then
			found = true
			break
		end
	end

	return found
end

local replace = function(str, pos, new)
	return ('%s%s%s'):format(str:sub(1, pos - 1), new, str:sub(pos + 1))
end

local getNext = function(str)
	local i = #str
	while i > 1 and str:sub(i, i) == 'z' do
		str = replace(str, i, 'a')
		i = i - 1
	end

	str = replace(str, i, string.char(str:sub(i, i):byte() + 1))
	return str
end

repeat
	str = getNext(str)
until isValid(str)

io.write(('New password: %s\n'):format(str))

D12P1.lua

local sum = 0
for line in io.lines('D12P1.txt') do
	line:gsub('([-]?%d+)', function(value)
		sum = sum + tonumber(value)
	end)
end

io.write(('Sum of all numbers: %d\n'):format(sum))

D13P1.lua

local data = {}
local people = {}

local who, value, whom

local contains = function(t, val)
	for _, v in pairs(t) do
		if v == val then
			return true
		end
	end

	return false
end

local getChange = function(who, whom)
	for _, v in pairs(data) do
		if v.who == who and v.whom == whom then
			return v.value
		end
	end

	for _, v in pairs(data) do
		if v.who == whom and v.whom == who then
			return v.value
		end
	end

	return 0
end

for line in io.lines('D13P1.txt') do
	who, value, whom = line:match('(%w+) would gain (%d+) happiness units by sitting next to (%w+)')
	if who == nil then
		who, value, whom = line:match('(%w+) would lose (%d+) happiness units by sitting next to (%w+)')
		if value ~= nil then
			value = -value
		end
	end

	table.insert(data, {
		who = who,
		whom = whom,
		value = tonumber(value)
	})

	if not contains(people, who) then
		table.insert(people, who)
	end

	if not contains(people, whom) then
		table.insert(people, whom)
	end
end

-- http://rosettacode.org/wiki/Permutations#Lua
local permutation
permutation = function(a, n, cb)
	if n == 0 then
		cb(a)
	else
		for i = 1, n do
			a[i], a[n] = a[n], a[i]
			permutation(a, n - 1, cb)
			a[i], a[n] = a[n], a[i]
		end
	end
end

local highest = 0
local current, total = 0, 0

permutation(people, #people, function(data)
	current, total = 0, 0
	for i = 1, #data do
		current = 0
		if i > 1 and i < #data then
			current = current + getChange(data[i], data[i + 1])
			current = current + getChange(data[i], data[i - 1])
		elseif i == 1 then
			current = current + getChange(data[i], data[i + 1])
			current = current + getChange(data[i], data[#data])
		else
			current = current + getChange(data[i], data[1])
			current = current + getChange(data[i], data[i - 1])
		end
		total = total + current
	end

	if total > highest then
		highest = total
	end
end)

io.write(('The most optimal change in happiness: %d'):format(highest))

D13P2.lua

-- NOTE: It's exactly the same as D13P1.lua
local data = {}
local people = {}

local who, value, whom

local contains = function(t, val)
	for _, v in pairs(t) do
		if v == val then
			return true
		end
	end

	return false
end

local getChange = function(who, whom)
	for _, v in pairs(data) do
		if v.who == who and v.whom == whom then
			return v.value
		end
	end

	for _, v in pairs(data) do
		if v.who == whom and v.whom == who then
			return v.value
		end
	end

	return 0
end

for line in io.lines('D13P2.txt') do
	who, value, whom = line:match('(%w+) would gain (%d+) happiness units by sitting next to (%w+)')
	if who == nil then
		who, value, whom = line:match('(%w+) would lose (%d+) happiness units by sitting next to (%w+)')
		if value ~= nil then
			value = -value
		end
	end

	table.insert(data, {
		who = who,
		whom = whom,
		value = tonumber(value)
	})

	if not contains(people, who) then
		table.insert(people, who)
	end

	if not contains(people, whom) then
		table.insert(people, whom)
	end
end

-- http://rosettacode.org/wiki/Permutations#Lua
local permutation
permutation = function(a, n, cb)
	if n == 0 then
		cb(a)
	else
		for i = 1, n do
			a[i], a[n] = a[n], a[i]
			permutation(a, n - 1, cb)
			a[i], a[n] = a[n], a[i]
		end
	end
end

local highest = 0
local current, total = 0, 0

permutation(people, #people, function(data)
	current, total = 0, 0
	for i = 1, #data do
		current = 0
		if i > 1 and i < #data then
			current = current + getChange(data[i], data[i + 1])
			current = current + getChange(data[i], data[i - 1])
		elseif i == 1 then
			current = current + getChange(data[i], data[i + 1])
			current = current + getChange(data[i], data[#data])
		else
			current = current + getChange(data[i], data[1])
			current = current + getChange(data[i], data[i - 1])
		end
		total = total + current
	end

	if total > highest then
		highest = total
	end
end)

io.write(('The most optimal change in happiness: %d'):format(highest))

D18P1.lua

local grid = {}
local steps = 100

local shift = {
	-- E
	{ 0,  1},
	-- W
	{ 0, -1},
	-- S
	{ 1,  0},
	-- N
	{-1,  0},
	-- NE
	{-1,  1},
	-- NW
	{-1, -1},
	-- SE
	{ 1,  1},
	-- SW
	{ 1, -1},
}

local getNeighbourCount = function(g, y, x)
	local count = 0
	local ny, nx = 0, 0

	for i = 1, #shift do
		ny = y + shift[i][1]
		nx = x + shift[i][2]

		if ny > 0 and ny <= #g and nx > 0 and nx <= #g then
			if g[ny][nx] then
				count = count + 1
			end
		end
	end

	return count
end

local index = 0
local ch

for line in io.lines('D18P1.txt') do
	index = index + 1

	grid[index] = {}
	for i = 1, #line do
		ch = line:sub(i, i)
		if ch == '#' then
			grid[index][i] = true
		elseif ch == '.' then
			grid[index][i] = false
		else
			io.write(('Unknown character at (%d, %d): %s\n'):format(index, i, ch))
		end
	end
end

local nc = 0
local ng = {}
for i = 1, steps do
	-- Iterate over the grid
	-- Temporary grid because we're supposed to check lights simultaneously
	for y = 1, #grid do
		ng[y] = {}
		for x = 1, #grid do
			nc = getNeighbourCount(grid, y, x)
			if grid[y][x] == true and (nc ~= 2 and nc ~= 3) then
				ng[y][x] = false
			elseif grid[y][x] == false and nc == 3 then
				ng[y][x] = true
			else
				ng[y][x] = grid[y][x]
			end
		end
	end

	-- Copy the grid (this can't be just grid = ng)
	for y = 1, #grid do
		for x = 1, #grid do
			grid[y][x] = ng[y][x]
		end
	end
end

-- Get the number of lights
local result = 0
for y = 1, #grid do
	for x = 1, #grid do
		if grid[y][x] then
			result = result + 1
		end
	end
end

io.write(('There are %d lights on after %d steps.\n'):format(result, steps))

D18P2.lua

local grid = {}
local steps = 100

local shift = {
	-- E
	{ 0,  1},
	-- W
	{ 0, -1},
	-- S
	{ 1,  0},
	-- N
	{-1,  0},
	-- NE
	{-1,  1},
	-- NW
	{-1, -1},
	-- SE
	{ 1,  1},
	-- SW
	{ 1, -1},
}

local isCorner = function(g, y, x)
	if y == 1 and x == 1 then
		return true
	end

	if y == 1 and x == #g then
		return true
	end

	if y == #g and x == 1 then
		return true
	end

	if y == #g and x == #g then
		return true
	end

	return false
end

local getNeighbourCount = function(g, y, x)
	local count = 0
	local ny, nx = 0, 0

	for i = 1, #shift do
		ny = y + shift[i][1]
		nx = x + shift[i][2]

		if ny > 0 and ny <= #g and nx > 0 and nx <= #g then
			if g[ny][nx] or isCorner(g, y, x) then
				count = count + 1
			end
		end
	end

	return count
end

local index = 0
local ch

for line in io.lines('D18P2.txt') do
	index = index + 1

	grid[index] = {}
	for i = 1, #line do
		ch = line:sub(i, i)
		if ch == '#' then
			grid[index][i] = true
		elseif ch == '.' then
			grid[index][i] = false
		else
			io.write(('Unknown character at (%d, %d): %s\n'):format(index, i, ch))
		end
	end
end

local nc = 0
local ng = {}
for i = 1, steps do
	-- Iterate over the grid
	-- Temporary grid because we're supposed to check lights simultaneously
	for y = 1, #grid do
		ng[y] = {}
		for x = 1, #grid do
			nc = getNeighbourCount(grid, y, x)
			if grid[y][x] == true and (nc ~= 2 and nc ~= 3) then
				ng[y][x] = false
			elseif grid[y][x] == false and nc == 3 then
				ng[y][x] = true
			else
				ng[y][x] = grid[y][x]
			end
		end
	end

	-- Copy the grid (this can't be just grid = ng)
	for y = 1, #grid do
		for x = 1, #grid do
			grid[y][x] = ng[y][x]
		end
	end
end

-- Get the number of lights
local result = 0
for y = 1, #grid do
	for x = 1, #grid do
		if grid[y][x] then
			result = result + 1
		end
	end
end

io.write(('There are %d lights on after %d steps.\n'):format(result, steps))

D1P1.lua

local str = '__your_input__'
local floor = 0
local ch

for i = 1, #str do
	ch = str:sub(i, i)
	if ch == ')' then
		floor = floor - 1
	elseif ch == '(' then
		floor = floor + 1
	end
end

io.write(('%d\n'):format(floor))

D1P2.lua

local str = '__your_input__'
local floor = 0
local ch

for i = 1, #str do
	ch = str:sub(i, i)
	if ch == ')' then
		floor = floor - 1
	elseif ch == '(' then
		floor = floor + 1
	end

	if floor == -1 then
		io.write(('Basement: %d\n'):format(i))
		break
	end
end

D23P1.lua

local program = {}
local pc = 1
local running = true

local registers = {
	a = 0,
	b = 0,
}

local setRegister = function(reg, value)
	registers[reg] = math.max(0, tonumber(value))
end

local getRegister = function(reg)
	return registers[reg]
end

local half = function(data)
	setRegister(data[1], getRegister(data[1]) / 2)
	return true
end

local triple = function(data)
	setRegister(data[1], getRegister(data[1]) * 3)
	return true
end

local increase = function(data)
	setRegister(data[1], getRegister(data[1]) + 1)
	return true
end

local jump = function(offset)
	if type(offset) == 'table' then
		pc = pc + tonumber(offset[1])
	else
		pc = pc + offset
	end
	return false
end

local jumpEven = function(data)
	if getRegister(data[1]) % 2 == 0 then
		return jump(tonumber(data[2]))
	end
	return true
end

local jumpOne = function(data)
	if getRegister(data[1]) == 1 then
		return jump(tonumber(data[2]))
	end
	return true
end

local getData = function(input)
	local data = {}
	input = input:sub(5):gsub(' ', '')
	input:gsub('([^,]+)', function(part)
		table.insert(data, part)
	end)
	return data
end

local lookup = {
	['hlf'] = half,
	['tpl'] = triple,
	['inc'] = increase,
	['jmp'] = jump,
	['jie'] = jumpEven,
	['jio'] = jumpOne,
}

local parse = function(line)
	local instruction = line:sub(1, 3)
	local data = getData(line)

	local func = lookup[instruction]
	local ret

	if func then
		ret = func(data)
	else
		running = false
	end

	return ret
end

for line in io.lines('D23P1.txt') do
	table.insert(program, line)
end

while running and pc <= #program do
	if parse(program[pc]) then
		pc = pc + 1
	end
end

io.write(('Registers\nA: %d\nB: %d\n'):format(registers.a, registers.b))

D23P2.lua

local program = {}
local pc = 1
local running = true

local registers = {
	a = 1,
	b = 0,
}

local setRegister = function(reg, value)
	registers[reg] = math.max(0, tonumber(value))
end

local getRegister = function(reg)
	return registers[reg]
end

local half = function(data)
	setRegister(data[1], getRegister(data[1]) / 2)
	return true
end

local triple = function(data)
	setRegister(data[1], getRegister(data[1]) * 3)
	return true
end

local increase = function(data)
	setRegister(data[1], getRegister(data[1]) + 1)
	return true
end

local jump = function(offset)
	if type(offset) == 'table' then
		pc = pc + tonumber(offset[1])
	else
		pc = pc + offset
	end
	return false
end

local jumpEven = function(data)
	if getRegister(data[1]) % 2 == 0 then
		return jump(tonumber(data[2]))
	end
	return true
end

local jumpOne = function(data)
	if getRegister(data[1]) == 1 then
		return jump(tonumber(data[2]))
	end
	return true
end

local getData = function(input)
	local data = {}
	input = input:sub(5):gsub(' ', '')
	input:gsub('([^,]+)', function(part)
		table.insert(data, part)
	end)
	return data
end

local lookup = {
	['hlf'] = half,
	['tpl'] = triple,
	['inc'] = increase,
	['jmp'] = jump,
	['jie'] = jumpEven,
	['jio'] = jumpOne,
}

local parse = function(line)
	local instruction = line:sub(1, 3)
	local data = getData(line)

	local func = lookup[instruction]
	local ret

	if func then
		ret = func(data)
	else
		running = false
	end

	return ret
end

for line in io.lines('D23P2.txt') do
	table.insert(program, line)
end

while running and pc <= #program do
	if parse(program[pc]) then
		pc = pc + 1
	end
end

io.write(('Registers\nA: %d\nB: %d\n'):format(registers.a, registers.b))

D2P1.lua

local width, height, length
local a, b, c, min
local total = 0

local getMin = function(a, b, c)
	return math.min(math.min(a, b), c)
end

for line in io.lines('D2P1.txt') do
	width, height, length = line:match('(%d+)x(%d+)x(%d+)')

	a = length * width
	b = width * height
	c = height * length
	min = getMin(a, b, c)

	total = total + 2 * a + 2 * b + 2 * c + min
end

io.write(('Total paper needed: %d sqft\n'):format(total))

D2P2.lua

local width, height, length
local a, b
local total = 0

local getTwoMin = function(...)
	local t = {...}
	table.sort(t, function(a, b)
		return tonumber(a) < tonumber(b)
	end)

	return t[1], t[2]
end

for line in io.lines('D2P2.txt') do
	width, height, length = line:match('(%d+)x(%d+)x(%d+)')

	-- Present
	a, b = getTwoMin(width, height, length)
	total = total + a * 2 + b * 2

	-- Bow
	total = total + width * height * length
end

io.write(('Total ribbon needed: %d ft\n'):format(total))

D3P1.lua

local getData = function()
	local f = io.open('D3P1.txt', 'r')
	local data = f:read('*all'):gsub('%s*$', '')
	f:close()
	return data
end

local contains = function(t, v)
	for _, tmp in pairs(t) do
		if v == tmp then
			return true
		end
	end

	return false
end

local str = getData()
local visited = {}
local houses = 1

local dir
local hash

local x, y = 0, 0
table.insert(visited, ('%dx%d'):format(x, y))

for i = 1, #str do
	dir = str:sub(i, i)
	if dir == '^' then
		y = y - 1
	elseif dir == 'v' then
		y = y + 1
	elseif dir == '<' then
		x = x - 1
	else
		x = x + 1
	end

	hash = ('%dx%d'):format(x, y)
	if not contains(visited, hash) then
		houses = houses + 1
		table.insert(visited, hash)
	end
end

io.write(('Visited houses: %d\n'):format(houses))

D3P2.lua

local getData = function()
	local f = io.open('D3P1.txt', 'r')
	local data = f:read('*all'):gsub('%s*$', '')
	f:close()
	return data
end

local contains = function(t, v)
	for _, tmp in pairs(t) do
		if v == tmp then
			return true
		end
	end

	return false
end

local str = getData()
local visited = {}
local houses = 1

local dir
local hash

local x, y, n = {0, 0}, {0, 0}, 1
table.insert(visited, ('%dx%d'):format(x[1], y[1]))

for i = 1, #str do
	n = ((i - 1) % 2) + 1
	dir = str:sub(i, i)
	if dir == '^' then
		y[n] = y[n] - 1
	elseif dir == 'v' then
		y[n] = y[n] + 1
	elseif dir == '<' then
		x[n] = x[n] - 1
	else
		x[n] = x[n] + 1
	end

	hash = ('%dx%d'):format(x[n], y[n])
	if not contains(visited, hash) then
		houses = houses + 1
		table.insert(visited, hash)
	end
end

io.write(('Visited houses: %d\n'):format(houses))

D4P1.lua

-- NOTE: Requires luacrypto module
-- luarocks install luacrypto
local crypto = require 'crypto'

local str = '__your_input__'

local input, digest
local i = 0

while true do
	input = ('%s%d'):format(str, i)
	digest = crypto.digest('md5', input, false)

	if digest:sub(1, 5) == '00000' then
		io.write(('Solution found.\nInput: %s\nDigest: %s\nNumber: %d\n'):format(input, digest, i))
		break
	end

	i = i + 1
end

D4P2.lua

-- NOTE: Requires luacrypto module
-- luarocks install luacrypto
local crypto = require 'crypto'

local str = '__your_input__'

local input, digest
local i = 0

while true do
	input = ('%s%d'):format(str, i)
	digest = crypto.digest('md5', input, false)

	if digest:sub(1, 6) == '000000' then
		io.write(('Solution found.\nInput: %s\nDigest: %s\nNumber: %d\n'):format(input, digest, i))
		break
	end

	i = i + 1
end

D5P1.lua

local vowels = 3
local blacklist = {'ab', 'cd', 'pq', 'xy'}

local getVowelCount = function(str)
	local _, count = str:gsub('[aeiou]', '')
	return count
end

local hasDoubles = function(str)
	local ch1, ch2

	for i = 1, (#str - 1) do
		ch1 = str:sub(i, i)
		ch2 = str:sub(i + 1, i + 1)
		if ch1 == ch2 then
			return true
		end
	end

	return false
end

local hasBlacklistedSeq = function(str)
	for _, v in pairs(blacklist) do
		if str:find(v) ~= nil then
			return true
		end
	end

	return false
end

local nice = 0
for line in io.lines('D5P1.txt') do
	if getVowelCount(line) >= vowels and hasDoubles(line) and not hasBlacklistedSeq(line) then
		nice = nice + 1
	end
end

io.write(('Nice words: %d\n'):format(nice))

D5P2.lua

-- It contains a pair of any two letters that appears at least twice in
-- the string without overlapping, like xyxy (xy) or aabcdefgaa (aa), but
-- not like aaa (aa, but it overlaps).
local cond1 = function(str)
	local ch1, ch2
	for i = 1, (#str - 1) do
		ch1 = str:sub(i, i)
		ch2 = str:sub(i + 1, i + 1)

		if str:find(('%s%s'):format(ch1, ch2), i + 2) ~= nil then
			return true
		end
	end

	return false
end

-- It contains at least one letter which repeats with exactly one letter
-- between them, like xyx, abcdefeghi (efe), or even aaa.
local cond2 = function(str)
	local ch1, ch2
	for i = 1, (#str - 2) do
		ch1 = str:sub(i, i)
		ch2 = str:sub(i + 2, i + 2)

		if ch1 == ch2 then
			return true
		end
	end

	return false
end

local nice = 0
for line in io.lines('D5P2.txt') do
	if cond1(line) and cond2(line) then
		nice = nice + 1
	end
end

io.write(('Nice words: %d\n'):format(nice))

D6P1.lua

local lights = {}
for x = 0, 999 do
	lights[x] = {}
	for y = 0, 999 do
		lights[x][y] = false
	end
end

local from, to = {}, {}
for line in io.lines('D6P1.txt') do
	-- Toggle
	from[1], from[2], to[1], to[2] = line:match('toggle (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				if lights[x][y] then
					lights[x][y] = false
				else
					lights[x][y] = true
				end
			end
		end
	end

	-- Turn on
	from[1], from[2], to[1], to[2] = line:match('turn on (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				lights[x][y] = true
			end
		end
	end

	-- Turn off
	from[1], from[2], to[1], to[2] = line:match('turn off (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				lights[x][y] = false
			end
		end
	end
end

local total = 0
for x = 0, 999 do
	for y = 0, 999 do
		if lights[x][y] then
			total = total + 1
		end
	end
end

io.write(('Total lights lit: %d\n'):format(total))

D6P2.lua

local brightness = {}
for x = 0, 999 do
	brightness[x] = {}
	for y = 0, 999 do
		brightness[x][y] = 0
	end
end

local from, to = {}, {}
for line in io.lines('D6P2.txt') do
	-- Toggle
	from[1], from[2], to[1], to[2] = line:match('toggle (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				brightness[x][y] = brightness[x][y] + 2
			end
		end
	end

	-- Turn on
	from[1], from[2], to[1], to[2] = line:match('turn on (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				brightness[x][y] = brightness[x][y] + 1
			end
		end
	end

	-- Turn off
	from[1], from[2], to[1], to[2] = line:match('turn off (%d+),(%d+) through (%d+),(%d+)')
	if from[1] ~= nil then
		for x = from[1], to[1] do
			for y = from[2], to[2] do
				brightness[x][y] = math.max(0, brightness[x][y] - 1)
			end
		end
	end
end

local total = 0
for x = 0, 999 do
	for y = 0, 999 do
		total = total + brightness[x][y]
	end
end

io.write(('Total brightness: %d\n'):format(total))

D7P1.lua

-- NOTE: Requires Lua 5.3
local wires = {}

local getValue = function(wire)
	return wires[wire]
end

local setValue = function(wire, v)
	wires[wire] = v & 65535
end

local getResult = function(a, b, op)
	local res = 0
	if op == 'AND' then
		res = a & b
	elseif op == 'OR' then
		res = a | b
	elseif op == 'LSHIFT' then
		res = a << b
	elseif op == 'RSHIFT' then
		res = a >> b
	end

	return res
end

local wire, lhs, op, rhs
local a, b

local lines = {}
for line in io.lines('D7P1.txt') do
	table.insert(lines, line)
end

while getValue('a') == nil do
	for _, line in pairs(lines) do
		-- Set signal
		lhs, wire = line:match('^(%S+) %-%> (%S+)$')
		if lhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			if a ~= nil then
				setValue(wire, a)
			end
		end

		-- AND, OR, LSHIFT and RSHIFT
		lhs, op, rhs, wire = line:match('^(%S+) (%S+) (%S+) %-%> (%S+)$')
		if lhs and op and rhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			b = tonumber(rhs)
			if b == nil then
				b = getValue(rhs)
			end

			if a ~= nil and b ~= nil then
				setValue(wire, getResult(a, b, op))
			end
		end

		-- NOT
		lhs, wire = line:match('^NOT (%S+) %-%> (%S+)$')
		if lhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			if a ~= nil then
				setValue(wire, ~a)
			end
		end
	end
end

io.write(('The signal provided to wire "a" is: %d\n'):format(getValue('a')))

D7P2.lua

-- NOTE: Requires Lua 5.3
-- It is exactly the same as D7P1.lua
local wires = {}

local getValue = function(wire)
	return wires[wire]
end

local setValue = function(wire, v)
	wires[wire] = v & 65535
end

local getResult = function(a, b, op)
	local res = 0
	if op == 'AND' then
		res = a & b
	elseif op == 'OR' then
		res = a | b
	elseif op == 'LSHIFT' then
		res = a << b
	elseif op == 'RSHIFT' then
		res = a >> b
	end

	return res
end

local wire, lhs, op, rhs
local a, b

local lines = {}
for line in io.lines('D7P2.txt') do
	table.insert(lines, line)
end

while getValue('a') == nil do
	for _, line in pairs(lines) do
		-- Set signal
		lhs, wire = line:match('^(%S+) %-%> (%S+)$')
		if lhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			if a ~= nil then
				setValue(wire, a)
			end
		end

		-- AND, OR, LSHIFT and RSHIFT
		lhs, op, rhs, wire = line:match('^(%S+) (%S+) (%S+) %-%> (%S+)$')
		if lhs and op and rhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			b = tonumber(rhs)
			if b == nil then
				b = getValue(rhs)
			end

			if a ~= nil and b ~= nil then
				setValue(wire, getResult(a, b, op))
			end
		end

		-- NOT
		lhs, wire = line:match('^NOT (%S+) %-%> (%S+)$')
		if lhs and wire then
			a = tonumber(lhs)
			if a == nil then
				a = getValue(lhs)
			end

			if a ~= nil then
				setValue(wire, ~a)
			end
		end
	end
end

io.write(('The signal provided to wire "a" is: %d\n'):format(getValue('a')))

D8P1.lua

local code, value = 0, 0
local tmp

local convert = function(value)
	return string.char(tonumber(value, 16))
end

for line in io.lines('D8P1.txt') do
	code = code + #line

	tmp = line:sub(2, #line - 1)
	tmp = tmp:gsub('\\"', '"')
	tmp = tmp:gsub('([^\\])\\\\x(%x%x)', '%1\\X%2')
	tmp = tmp:gsub('\\\\', '\\')
	tmp = tmp:gsub('\\x(%x%x)', convert)

	value = value + #tmp
end

io.write(('Original: %d\nDecoded: %d\nResult: %d\n'):format(code, value, code - value))

D8P2.lua

local code, value = 0, 0

for line in io.lines('D8P2.txt') do
	code = code + #line
	value = value + #('%q'):format(line)
end

io.write(('Original: %d\nEncoded: %d\nResult: %d'):format(code, value, value - code))

D9P1.lua

local data = {}
local cities = {}

local from, to, distance

local contains = function(t, val)
	for _, v in pairs(t) do
		if v == val then
			return true
		end
	end

	return false
end

local getDistance = function(from, to)
	for _, v in pairs(data) do
		if v.from == from and v.to == to then
			return v.distance
		end
	end

	for _, v in pairs(data) do
		if v.from == to and v.to == from then
			return v.distance
		end
	end

	return 0
end

-- http://rosettacode.org/wiki/Permutations#Lua
local permutation
permutation = function(a, n, cb)
	if n == 0 then
		cb(a)
	else
		for i = 1, n do
			a[i], a[n] = a[n], a[i]
			permutation(a, n - 1, cb)
			a[i], a[n] = a[n], a[i]
		end
	end
end

for line in io.lines('D9P1.txt') do
	from, to, distance = line:match('(%S+) to (%S+) = (%d+)')
	table.insert(data, {
		from = from,
		to = to,
		distance = distance
	})

	if not contains(cities, from) then
		table.insert(cities, from)
	end

	if not contains(cities, to) then
		table.insert(cities, to)
	end
end

local shortest = 99999 -- Whatcha gonna do about it, nerd?
permutation(cities, #cities, function(data)
	local distance = 0
	for i = 1, #data - 1 do
		distance = distance + getDistance(data[i], data[i + 1])
	end

	if distance < shortest then
		shortest = distance
	end

	-- Uncomment to see the list of all routes (will take significantly longer due to I/O and table.concat)
	-- io.write(('%s: %d\n'):format(table.concat(data, ' -> '), distance))
end)

io.write(('Shortest distance: %d\n'):format(shortest))

D9P2.lua

local data = {}
local cities = {}

local from, to, distance

local contains = function(t, val)
	for _, v in pairs(t) do
		if v == val then
			return true
		end
	end

	return false
end

local getDistance = function(from, to)
	for _, v in pairs(data) do
		if v.from == from and v.to == to then
			return v.distance
		end
	end

	for _, v in pairs(data) do
		if v.from == to and v.to == from then
			return v.distance
		end
	end

	return 0
end

-- http://rosettacode.org/wiki/Permutations#Lua
local permutation
permutation = function(a, n, cb)
	if n == 0 then
		cb(a)
	else
		for i = 1, n do
			a[i], a[n] = a[n], a[i]
			permutation(a, n - 1, cb)
			a[i], a[n] = a[n], a[i]
		end
	end
end

for line in io.lines('D9P2.txt') do
	from, to, distance = line:match('(%S+) to (%S+) = (%d+)')
	table.insert(data, {
		from = from,
		to = to,
		distance = distance
	})

	if not contains(cities, from) then
		table.insert(cities, from)
	end

	if not contains(cities, to) then
		table.insert(cities, to)
	end
end

local longest = 0
permutation(cities, #cities, function(data)
	local distance = 0
	for i = 1, #data - 1 do
		distance = distance + getDistance(data[i], data[i + 1])
	end

	if distance > longest then
		longest = distance
	end

	-- Uncomment to see the list of all routes (will take significantly longer due to I/O and table.concat)
	-- io.write(('%s: %d\n'):format(table.concat(data, ' -> '), distance))
end)

io.write(('Longest distance: %d\n'):format(longest))