:grey_exclamation:Day 11 Solution Thread:heavy_hea...

# advent-of-code

[bjonnh]

❕Day 11 Solution Thread❣️

[David Whittaker]

Ah, I knew there would be a Game of Life in there on one of the days!

[David Whittaker]

Darn off-by-one errors crushed me on this

[ephemient]

https://github.com/ephemient/aoc2020/blob/main/kt/src/main/kotlin/io/github/ephemient/aoc2020/Day11.kt

[ephemient]

these are starting to get too unwieldy to copy-paste into slack

[andyb]

I reused a Grid2D class (created for AoC 2018) which wraps <Array<Array<Char>>> and provides Direction & Coord classes.

I had to add some extra methods Grid2D.firstSeats() & Grid2D.firstSeatInDirection() shown in the snippet to solve Part 2.

SeatingSystem

[Nir]

Untitled

[Nir]

debating whether to go back and refactor this to make it "pretty". I did most stuff in the original solution with pretty raw for loops and integers (well, the hard part at least)

[Nir]

I tried refactoring a bit, Kotlin seems to complain here because the type after the map is Sequence<Any> rather than Sequence<Int>. Can anyone point out the easiest way to solve this? Is my return qualified correctly?

fun SeatMap.visibleNeighbors(p: Point) = directionPoints().map {
    var point = p
    while (true) {
        point += it
        if (point !in this || getSeat(point) == Seat.EMPTY) {
            return@map 0
        }
        if (getSeat(point) == Seat.OCCUPIED) {
            return@map 1
        }
    }
}.sum()

[Nir]

hmm, if I add a 0 on the last line of the map it compiles 😞 Any less awkward solution?

[Nir]

In the end I ended up refactoring to this more functional approach:

fun SeatMap.visibleNeighbors(p: Point) = directionPoints().map { dirPoint ->

    val first = generateSequence(p + dirPoint) { it + dirPoint }
        .filter { getSeat(it) != Seat.EMPTY }
        .first()

    when (getSeat(first)) {
        null, Seat.EMPTY -> 0
        Seat.OCCUPIED -> 1
        else -> throw Exception("")
    }
}.sum()

[ephemient]

re while (true), https://youtrack.jetbrains.com/issue/KT-24191

[todd.ginsberg]

Blog: https://todd.ginsberg.com/post/advent-of-code/2020/day11/

Code: https://github.com/tginsberg/advent-2020-kotlin/blob/main/src/main/kotlin/com/ginsberg/advent2020/Day11.kt

[todd.ginsberg]

I took today off work because I'm using up vacation time that goes away at the end of the year, so I took my time with this one. I'm pretty happy with how that turned out.