Advent of Code 2020 Day 12

advent-of-code-2020-day-12.js

const puzzleInput = ``

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

// Part 1
const nextDir = (facing, going, amount) => {
  const clockwise = 'NESW'
  const facingIndex = clockwise.indexOf(facing)
  if (going === 'L') {
    amount = 360 - amount
  }
  const goingIndex = (facingIndex + (amount / 90)) % clockwise.length
  return clockwise[goingIndex]
}

const moveByDirection = (acc, dir, amount) => {
  switch (dir) {
    case 'N': return acc.y -= amount
    case 'S': return acc.y += amount
    case 'E': return acc.x += amount
    case 'W': return acc.x -= amount
    case 'F': return moveByDirection(acc, acc.facing, amount)
    default: return acc.facing = nextDir(acc.facing, dir, amount)
  }
}

const parseInstruction = (acc, instruction) => {
  const dir = instruction[0]
  const amount = parseInt(instruction.substr(1))
  moveByDirection(acc, dir, amount)
  return acc
}

const partOne = (input) => {
  const instructions = parseInput(input)
  const distance = instructions.reduce(parseInstruction, { x: 0, y: 0, facing: 'E' })
  console.log(Math.abs(distance.x) + Math.abs(distance.y))
}

partOne(puzzleInput)

// Part 2
const moveFerry = (acc, amount) => {
  acc.ferry.x += (acc.waypoint.x * amount)
  acc.ferry.y += (acc.waypoint.y * amount)
}

const rotateWaypoint = (acc, dir, amount) => {
  let { x, y } = acc.waypoint
  const steps = Math.floor((dir === 'R' ? amount : (360 - amount)) / 90)
  for (let i = 0; i < steps; i++) {
    acc.waypoint.x = y * -1
    acc.waypoint.y = x
    x = acc.waypoint.x
    y = acc.waypoint.y
  }
}

const moveCorrectly = (acc, dir, amount) => {
  switch (dir) {
    case 'N': return acc.waypoint.y -= amount
    case 'S': return acc.waypoint.y += amount
    case 'E': return acc.waypoint.x += amount
    case 'W': return acc.waypoint.x -= amount
    case 'F': return moveFerry(acc, amount)
    default: return rotateWaypoint(acc, dir, amount)
  }
}

const navigate = (acc, instruction) => {
  const dir = instruction[0]
  const amount = parseInt(instruction.substr(1))
  moveCorrectly(acc, dir, amount)
  return acc
}

const partTwo = (input) => {
  const instructions = parseInput(input)
  const result = instructions.reduce(navigate, {
    waypoint: { x: 10, y: -1 },
    ferry: { x: 0, y: 0 },
  })
  const distance = Math.abs(result.ferry.x) + Math.abs(result.ferry.y)
  console.log(distance)
}

partTwo(puzzleInput)