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Advent of code - Day 17

qmenoret profile image Quentin Ménoret ・3 min read

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.

For this one, I'm not going to lie... I cheated!
I actually updated the input manually, and generated a big enough map... So I didn't have to handle infinite size! Since we know that there are at most 6 cycles, then the end size of each size if the original plus and minus 6.

It's definitely not a solution that is easy to extend (far from generic) but... It works in this case!

Here is my solution for day #17:

let input = `.................................................
.................................................
.................................................
.................................................
....................##.####......................
....................#.....#......................
...................#.###.##......................
...................#####.##......................
...................#...##.#......................
...................#######.......................
...................##.#####......................
....................##...#.......................
.................................................
.................................................
.................................................
.................................................
.................................................`
  .split('\n')
  .map((x) => x.split(''))

// Here I'm generating the "bigger" map
input = [
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input,
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
  input.map((x) => x.map((y) => '.')),
]

input = [
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input,
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
  input.map((x) => x.map((y) => y.map((y) => '.'))),
]

function getNeighbours(coordinates) {
  return _getNeighbours(coordinates).filter((n) => !n.every((x, index) => x === coordinates[index]))
}

function _getNeighbours(coordinates) {
  if (coordinates.length === 1) return [-1, 0, 1].map((x) => [coordinates[0] + x])
  const result = _getNeighbours(coordinates.slice(1))

  return [
    ...result.map((r) => [coordinates[0] - 1, ...r]),
    ...result.map((r) => [coordinates[0], ...r]),
    ...result.map((r) => [coordinates[0] + 1, ...r]),
  ]
}

function next(state) {
  return state.map((yLayer, x) => {
    return yLayer.map((zLayer, y) => {
      return zLayer.map((wLayer, z) => {
        return wLayer.map((element, w) => {
          const neighbours = getNeighbours([x, y, z, w])
          const count = neighbours.reduce((acc, [x, y, z, w]) => {
            if (!state[x] || !state[x][y] || !state[x][y][z] || !state[x][y][z][w]) return acc
            if (state[x][y][z][w] === '#') return acc + 1
            return acc
          }, 0)
          if (count === 3) return '#'
          if (element === '#' && count === 2) return '#'
          return '.'
        })
      })
    })
  })
}

const finalState = [0, 1, 2, 3, 4, 5].reduce((state) => {
  let next1 = next(state)
  return next1
}, input)

const count = finalState.reduce(
  (acc, xLayer) =>
    acc +
    xLayer.reduce(
      (acc, yLayer) =>
        acc +
        yLayer.reduce((acc, wLayer) => acc + wLayer.reduce((acc, element) => acc + (element === '#' ? 1 : 0), 0), 0),
      0,
    ),
  0,
)

console.log(count)
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Feel free to share your solution in the comments!


Photo by Markus Spiske on Unsplash

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