Advent of Code 2020 Day 10

advent-of-code-2020-day-10.js

const puzzleInput = ``

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

const getDifferences = (adapters) => {
  return adapters.map((adapter, index) => {
    let prev = adapters[index - 1] || 0
    return adapter - prev
  })
}

const countDifferences = (differences) => {
  return differences.reduce((acc, diff) => {
    ++acc[diff]
    return acc
  }, { 1: 0, 3: 1 })
}

const partOne = (input) => {
  const adapters = parseInput(input).sort((a, b) => a - b)
  const differences = getDifferences(adapters)
  const values = countDifferences(differences)
  console.log(values[1] * values[3])
}

partOne(puzzleInput)

// Part 2
const prevThree = (adapters, index) => {
  return [1, 2, 3].map(x => adapters[index - x] || 0)
}

const partTwo = (input) => {
  const adapters = parseInput(input).sort((a, b) => b - a)
  adapters.unshift(adapters[0] + 3)
  adapters.push(0)
  const configurations = [1]
  for (let index = 1; index < adapters.length; index++) {
    const adapter = adapters[index]
    const config = prevThree(adapters, index).reduce((acc, prev, offset) => {
      const prevIndex = index - offset - 1
      return acc + ((prev - adapter < 4) ? (configurations[prevIndex] || 0) : 0)
    }, 0)
    configurations.push(config)
  }

  console.log(configurations[configurations.length - 1])
}

partTwo(puzzleInput)