Advent of code - Day 15

Are you participating in the Advent of code this year?

If you don't know what the advent of code is, it's a website where you'll find a daily challenge (every day it gets harder). It's a really fun event, you should participate!

I try to solve the exercises using either JavaScript or TypeScript and will share my solutions daily (with one day delay so no one can cheat!). I only share the solution for the second part.

Ok, I'm pretty sure they decided to give us a break following the weekend that was way harder than the rest! Good for us, this one was pretty simple.

Here is my solution for day #15:

const input = `14,1,17,0,3,20`.split(',')

// Pre alloc the array for performance
const record = new Array(30000000)

function process(number, index) {
  const firstSeen = record[number] === undefined
  const seen = record[number]
  record[number] = index
  return firstSeen ? 0 : index - seen
}

let lastSeenWas = 0
for (let i = 0; i < input.length; i++) lastSeenWas = process(input[i], i)

for (let i = input.length; i < 30000000 - 1; i++) {
  lastSeenWas = process(lastSeenWas, i)
}

console.log(lastSeenWas)

Feel free to share your solution in the comments!

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Photo by Markus Spiske on Unsplash