2024 Day 8 · advent of code · Zulip Chat Archive

Stream: advent of code

Topic: 2024 Day 8

Oskar Hahn (Dec 08 2024 at 07:59):

Here is mine: https://github.com/ostcar/aoc2024/blob/main/day08.roc

part1 in 1.747ms
part2 in 4.987ms

It took me some time, because I did all the bugs that are even possible.

One of them was this

input
        |> Str.splitOn "\n"
        |> List.walkWithIndex (Dict.empty {}) \acc, line, row ->
            line
            |> Str.toUtf8
            |> List.walkWithIndex acc \acc2, char, col ->
                if char == '.' then
                    acc
                    else

                acc2
                |> Dict.update char \value ->
                    value
                    |> Result.withDefault []
                    |> List.append { row: row |> Num.toI64, col: col |> Num.toI64 }
                    |> Ok

Can you see it? It took me around have of an hour. Hint: This bug will not happen anymore, when shadowing is allowed.

Brendan Hansknecht (Dec 08 2024 at 08:09):

The fun of number suffixes

Brendan Hansknecht (Dec 08 2024 at 08:10):

I occasionally pulled certain lambdas into separate top level functions to avoid naming issues like that.

Robin Camarasa (Dec 08 2024 at 10:14):

Today went smoothly, getting more and more confortable with the standard library :)
https://github.com/RobinCamarasa/Advent-of-code/blob/master/2024/day08/RobinCamarasa/main.roc

Luke Boswell (Dec 08 2024 at 10:22):

Here's my solution... only made it as far as part 1 so far.

https://github.com/lukewilliamboswell/aoc/blob/main/2024/08.roc

TIMING:
READING INPUT:  <1ms
SOLVING PART 1: 2ms

Nicola Peduzzi (Dec 08 2024 at 10:37):

Done for me too https://github.com/thenikso/advent-of-code-2024-roc/blob/main/08.roc

Day 08 part 1: (Ok ...) [1ms]
Day 08 part 2: (Ok ...) [1ms]

Using again the excellent Array2D

Anthony Bullard (Dec 08 2024 at 19:55):

Just about to start on this. Can someone explain this sentence from Part 1?

In particular, an antinode occurs at any point that is perfectly in line with two antennas of the same frequency - but only when one of the antennas is twice as far away as the other

Specifically that last clause

Anthony Bullard (Dec 08 2024 at 19:55):

Looking at the examples, it doesn't seem to really mean anything?

Paul Stanley (Dec 08 2024 at 20:02):

I think it means: an antinode exists at a point directly in line with two antennas and as far from the nearest antenna as they are from each other. So if two antennas are due north/south and 2 rows apart, an antinode will occur at the point due north and 2 rows above the northern one, and due south and 2 rows below the southern one.

Anthony Bullard (Dec 08 2024 at 20:34):

Thanks. That’s what I deduced from the example, but I still can’t parse that sentence to mean that :joy:

Paul Stanley (Dec 08 2024 at 20:35):

I don't disagree! It's a very confused way of explaining.

Anthony Bullard (Dec 09 2024 at 15:18):

Sometimes you add debugger statements, and they lead you down an hour long rabbit hole before you figure out that the output is not what you think :rofl:

Anthony Bullard (Dec 09 2024 at 15:19):

https://github.com/gamebox/aoc-2024/tree/main/day8

Anthony Bullard (Dec 09 2024 at 15:25):

This instrumentation tells me both parts take less than 1ns, which does not seem right...

main =
    now = Utc.now! {}
    p1Start = Utc.toNanosSinceEpoch now
    total = getTotal realInput
    p1End =
        Utc.now! {}
        |> Utc.toNanosSinceEpoch
    part2 = getPart2Total realInput
    p2End =
        Utc.now! {}
        |> Utc.toNanosSinceEpoch
    Stdout.line! "There are $(Num.toStr total) obstacles, and $(Num.toStr part2) with harmonics."
    Stdout.line! "Part 1: $(Num.toStr (p1End - p1Start))ns"
    Stdout.line! "Part 2: $(Num.toStr (p2End - p1End))ns"

Anthony Bullard (Dec 09 2024 at 15:25):

Is that expected?

Anton (Dec 09 2024 at 16:08):

I don't see anything wrong with the calculation, you can paste your solution in Luke's aoc tempplate to compare measurements

Brendan Hansknecht (Dec 09 2024 at 18:36):

@Anthony Bullard this is testing with the input.txt in the repo?

Anthony Bullard (Dec 09 2024 at 18:43):

Yeah with optimized build

Anthony Bullard (Dec 09 2024 at 18:43):

I definitely did NOT build my solution with perf in mind

Brendan Hansknecht (Dec 09 2024 at 18:46):

Utc.toNanosSinceEpoch

At least for me on mac, the timer we are based off of is only timing in microseconds. I either see:

There are 305 obstacles, and 1150 with harmonics.
Part 1: 0ns
Part 2: 0ns

or:

There are 305 obstacles, and 1150 with harmonics.
Part 1: 1000ns
Part 2: 0ns

Brendan Hansknecht (Dec 09 2024 at 18:46):

Last 3 digits of printing out the nanoseconds is always zero

Anthony Bullard (Dec 09 2024 at 18:46):

That's what I was thinking

Anthony Bullard (Dec 09 2024 at 18:46):

So no greater precision than ms

Anthony Bullard (Dec 09 2024 at 18:47):

I'm also on Mac

Brendan Hansknecht (Dec 09 2024 at 18:47):

us, not ms, but yeah

Anthony Bullard (Dec 09 2024 at 18:47):

Makes sense, thanks for verifying that

Brendan Hansknecht (Dec 09 2024 at 18:48):

still runs within a microsecond which is quite fast for aoc in general

Anthony Bullard (Dec 09 2024 at 18:48):

Yeah, duh us

Anthony Bullard (Dec 09 2024 at 18:49):

Fast is nice for AOC, but never my first goal. Especially in a language I'm still learning

Brendan Hansknecht (Dec 09 2024 at 19:00):

Ah yeah, utc.time is based on SystemTime, which is not meant for measuring time elapsed. It is meant getting the current real world time. We should be basing time measurements on Instant.

With instant (I think wired correctly, but it is adhoc to send it through the utc.time api), I see:

Part 1: 2625ns
Part 2: 84ns

Brendan Hansknecht (Dec 09 2024 at 19:01):

So we may want a different timer tool in basic cli for differential time measurements.

Brendan Hansknecht (Dec 09 2024 at 19:01):

System time isn't even guaranteed to be monotonic (it can go backwards)

Brendan Hansknecht (Dec 09 2024 at 19:04):

Actually, sorry, this is correct timing. The early one had init issues (first one was measuring locking and initializing an OnceLock in rust):

Part 1: 84ns
Part 2: 83ns

Anthony Bullard (Dec 09 2024 at 19:27):

Thanks, seems like that should definitely be in the basic-cli platform

Anthony Bullard (Dec 09 2024 at 19:28):

WHich reminds me ... every been any talk of working out a common interface for common types across platforms - like a POSIX for Roc platforms ? Not mandatory, but most non-client oriented platforms would strive to implement it (same interface in Roc that is)

Anthony Bullard (Dec 09 2024 at 19:29):

That way if I use File in basic-cli, I could expect to find the same API available in basic-webserver?

Brendan Hansknecht (Dec 09 2024 at 19:34):

It has been discussed a little. I have pushed for the idea of interfaces a few times. I think with static dispatch, we will get a solution (though not sure if it will be enough)

Luke Boswell (Dec 09 2024 at 20:48):

Anthony Bullard said:

WHich reminds me ... every been any talk of working out a common interface for common types across platforms - like a POSIX for Roc platforms ? Not mandatory, but most non-client oriented platforms would strive to implement it (same interface in Roc that is)

Richard has done a lot of design work on the path package, just needs implementation

https://github.com/roc-lang/path

Luke Boswell (Dec 09 2024 at 20:49):

He gave a presentation on it in this meetup https://roc.zulipchat.com/#narrow/channel/303057-gatherings/topic/Roc.20Online.20Meetup.20Aug.202024/near/464907794

Brendan Hansknecht (Dec 10 2024 at 08:03):

So we definitely have a lowering bug with Task ! and |>

main =
    now = Utc.now! {}
    p1Start = Utc.toNanosSinceEpoch now
    total = getTotal realInput
    p1End =
        Utc.now! {}
        |> Utc.toNanosSinceEpoch
    part2 = getPart2Total realInput
    p2End =
        Utc.now! {}
        |> Utc.toNanosSinceEpoch
    Stdout.line! "There are $(Num.toStr total) obstacles, and $(Num.toStr part2) with harmonics."
    Stdout.line! "Part 1: $(Num.toStr (p1End - p1Start))ns"
    Stdout.line! "Part 2: $(Num.toStr (p2End - p1End))ns"

This gives garbage times as if all of the Utc.now! are called back to back.
If you remove the |> and makes separate variables, the timings become reasonable.

Brendan Hansknecht (Dec 10 2024 at 08:05):

This should work:

main =
    now = Utc.now! {}
    p1Start = Utc.toNanosSinceEpoch now
    total = getTotal realInput
    p1EndTime = Utc.now! {}
    p1End = Utc.toNanosSinceEpoch p1EndTime
    part2 = getPart2Total realInput
    p2EndTime = Utc.now! {}
    p2End = Utc.toNanosSinceEpoch p2EndTime
    Stdout.line! "There are $(Num.toStr total) obstacles, and $(Num.toStr part2) with harmonics."
    Stdout.line! "Part 1: $(Num.toStr (p1End - p1Start))ns"
    Stdout.line! "Part 2: $(Num.toStr (p2End - p1End))ns"

Brendan Hansknecht (Dec 10 2024 at 08:06):

Not sure if this is a bug worth fixing cause it may go away with Task, but we should double check it isn't broken with purity inference.

Brendan Hansknecht (Dec 11 2024 at 18:08):

CC: @Anthony Bullard roc bug breaking timing and a workaround

Anthony Bullard (Dec 11 2024 at 18:09):

Thanks for looking into that @Brendan Hansknecht

Last updated: Jul 26 2025 at 12:14 UTC