Advent of Code 2019 - Day 2 in Lua

AoCday2.lua

local inspect = require 'inspect'

function table.clone(org)
  return {table.unpack(org)}
end

-- INPUTS --------------------

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

input1202 = {
  1,12,2,3,
  1,1,2,3,
  1,3,4,3,
  1,5,0,3,
  2,6,1,19,
  1,19,10,23,
  2,13,23,27,
  1,5,27,31,
  2,6,31,35,
  1,6,35,39,
  2,39,9,43,
  1,5,43,47,
  1,13,47,51,
  1,10,51,55,
  2,55,10,59,
  2,10,59,63,
  1,9,63,67,
  2,67,13,71,
  1,71,6,75,
  2,6,75,79,
  1,5,79,83,
  2,83,9,87,
  1,6,87,91,
  2,91,6,95,
  1,95,6,99,
  2,99,13,103,
  1,6,103,107,
  1,2,107,111,
  1,111,9,0,
  99,
  2,14,0,0
}

-- PART 1 ---------------------

function runIntcode(program)
  -- print('runIntcode')
  local p = program
  local readPos = 1

  function runLine(readPos)
    local opcode = p[readPos]
    -- print( 'running opcode: ' .. opcode )

    if opcode == 99 then
      return
    end

    local pos1 = p[readPos + 1] + 1
    local pos2 = p[readPos + 2] + 1
    local dest = p[readPos + 3] + 1
    -- print('pos1: ' .. pos1 .. ', pos2: ' .. pos2 .. ', dest: ' .. dest)
    
    if opcode == 1 then
      p[dest]= p[pos1] + p[pos2]
    elseif opcode == 2 then
      p[dest]= p[pos1] * p[pos2]
    else
      return 'error: invalid opcode'
    end

    readPos = readPos + 4
    -- opcode = p[readPos]
    runLine(readPos)
  end

  runLine(readPos)
  return p
end

-- -- TESTS
-- 1,0,0,0,99 becomes 2,0,0,0,99 (1 + 1 = 2).
test1 = {1,0,0,0,99}
print('test1 should be {2,0,0,0,99}: ' .. inspect(runIntcode(test1)))
-- 2,3,0,3,99 becomes 2,3,0,6,99 (3 * 2 = 6).
test2 = {2,3,0,3,99}
print('test2 should be {2,3,0,6,99}: ' .. inspect(runIntcode(test2)))
-- 2,4,4,5,99,0 becomes 2,4,4,5,99,9801 (99 * 99 = 9801).
test3 = {2,4,4,5,99,0}
print('test3 should be {2,4,4,5,99,9801}: ' .. inspect(runIntcode(test3)))
-- 1,1,1,4,99,5,6,0,99 becomes 30,1,1,4,2,5,6,0,99.
test4 = {1,1,1,4,99,5,6,0,99}
print('test4 should be {30,1,1,4,2,5,6,0,99}: ' .. inspect(runIntcode(test4)))

print('input1202 produces: ' .. inspect(runIntcode(input1202)))

-- PART 2 ------------------------------

function testNounVerbOutputProgram(noun, verb, output, program)
  local p = table.clone(program)
  p[2]= noun
  p[3]= verb
  -- print(inspect(p))
  local calc = runIntcode(p)
  -- print('calc: ' .. inspect(calc))
  -- print('calc[1]: ' .. calc[1] .. ', output: ' .. output)
  return calc[1] == output
end

print('Should be true: ' .. inspect(testNounVerbOutputProgram(12, 2, 4138687, input)))
print('Should be false: ' .. inspect(testNounVerbOutputProgram(20, 2, 4138687, input)))

function findNounAndVerbToProduce(val, program)
  local noun = 0
  local verb = 0
  for i = 0, 99 do
    noun = i
    for j = 0, 99 do
      verb = j
      if testNounVerbOutputProgram(noun, verb, val, program) then
        return noun, verb
      end
    end
  end
end

local n, v = findNounAndVerbToProduce(19690720, input)
print( 'noun and verb to produce 19690720: ' .. n, v )
local solution = 100 * n + v
print( 'solution: ' .. solution )

Okay I realize lines 149–158 don't need the variable declarations, and that if I DID need them, they should have been local!

for i = 0, 99 do
    for j = 0, 99 do
      if testNounVerbOutputProgram(i, j, val, program) then
        return i, j
      end
    end
end