Advent of Code 2020 Day 9

advent-of-code-2020-day-9.js

const puzzleInput = ``

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

const findInvalidNumber = (numbers) => {
  return numbers.reduce((acc, number, index) => {
    if (index < 25) { return acc }
    let found = null
    for (let i = -1; i>=-25; i--) {
      const target = number - numbers[index + i]
      found = numbers.slice(index - 25, index).find(x => x === target)
      if (found) { break }
    }
    return found ? acc : number
  }, 0)
}

const partOne = (input) => {
  const numbers = parseInput(input)
  const result = findInvalidNumber(numbers)
  console.log(result)
}

partOne(puzzleInput)

// Part 2
const findContiguousSum = (numbers, sum) => {
  for (let index = 0; index < numbers.length; index++) {
    let total = 0
    for (let subIndex = index; total < sum; subIndex++) {
      total += numbers[subIndex]
      if (total === sum) {
        const subset = numbers.slice(index, subIndex + 1).sort()
        return subset[0] + subset[subset.length - 1]
      }
    }
  }
}

const partTwo = (input) => {
  const numbers = parseInput(input)
  const invalid = findInvalidNumber(numbers)
  const weakness = findContiguousSum(numbers, invalid)
  console.log(weakness)
}

partTwo(puzzleInput)