Day2.lua

Day2

local inputString = require(script.Input)
local inputStringArray = inputString:split(",")

local ADD = 1
local MULTIPLY = 2

local opFunctions = {
	[ADD] = function(input1, input2)
		return input1 + input2
	end,
	[MULTIPLY] = function(input1, input2)
		return input1 * input2
	end,
}

function executeOp(array, opcode, input1Pointer, input2Pointer, returnPointer)
	local input1 = array[input1Pointer]
	local input2 = array[input2Pointer]

	array[returnPointer] = opFunctions[opcode](input1, input2)
end

function executeProgram(opArray)
	for i = 1, #opArray, 4 do
		local opcode = opArray[i]
		local input1Pointer = opArray[i+1] + 1
		local input2Pointer = opArray[i+2] + 1
		local returnPointer = opArray[i+3] + 1

		if opcode == 99 then
			return opArray[1]
		end

		executeOp(opArray, opcode, input1Pointer, input2Pointer, returnPointer)
	end
end

local function getInput(noun, verb)
	local inputArray = {}

	for k,v in ipairs(inputStringArray) do
		table.insert(inputArray, tonumber(v))
	end
	
	inputArray[2] = noun
	inputArray[3] = verb
	
	return inputArray
end

-- part 1 solution
local inputArray = getInput(12, 2)
local output = executeProgram(inputArray)
print("Part 1 solution:", output)

-- part 2 solution
local desiredOutput = 19690720

-- BRUTE FORCE
for noun = 0, 99 do
	for verb = 0, 99 do
		local output = executeProgram(getInput(noun, verb))
		
		if output == desiredOutput then
			print("Noun and verb are:", noun, verb)
			local solution = 100 * noun + verb
			print("Part 2 solution:", solution)
		end
	end
end

Input.lua

return [[1,0,0,3,1,1,2,3,1,3,4,3,1,5,0,3,2,1,6,19,1,19,5,23,2,13,23,27,1,10,27,31,2,6,31,35,1,9,35,39,2,10,39,43,1,43,9,47,1,47,9,51,2,10,51,55,1,55,9,59,1,59,5,63,1,63,6,67,2,6,67,71,2,10,71,75,1,75,5,79,1,9,79,83,2,83,10,87,1,87,6,91,1,13,91,95,2,10,95,99,1,99,6,103,2,13,103,107,1,107,2,111,1,111,9,0,99,2,14,0,0]]

rip nimblz