Advent of Code 2020 Day 8

advent-of-code-2020-day-8.js

const puzzleInput = ``

// Part 1
const parseInput = (input) => {
  return input.split(/\n/)
}

const interpretInstruction = (line) => {
  let [command, amount] = line.split(' ')
  return {
    amount: parseInt(amount),
    command,
  }
}

const runInstructions = (acc, instructions, index) => {
  const instruction = instructions[index]
  if (acc[index] || !instruction) { return { count: acc.count, loop: acc[index] } }
  acc[index] = true

  switch (instruction.command) {
    case 'jmp': return runInstructions(acc, instructions, index + instruction.amount)
    case 'acc': acc.count += instruction.amount
    default: return runInstructions(acc, instructions, index + 1)
  }
}

const partOne = (input) => {
  const instructions = parseInput(input).map(interpretInstruction)
  const result = runInstructions({ count: 0 }, instructions, 0)
  console.log(result.count)
}

partOne(puzzleInput)

// Part 2
const autoFixProgram = (instructions) => {
  return instructions.reduce((acc, instruction, index) => {
    if (!!acc || instruction.command === 'acc') { return acc }
    instruction.command = instruction.command === 'jmp' ? 'nop' : 'jmp'
    const result = runInstructions({ count: 0 }, instructions, 0)
    instruction.command = instruction.command === 'jmp' ? 'nop' : 'jmp'
    return result.loop ? acc : { count: result.count, index }
  }, null)
}

const partTwo = (input) => {
  const instructions = parseInput(input).map(interpretInstruction)
  const result = autoFixProgram(instructions)
  console.log(result && result.count)
}

partTwo(puzzleInput)