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## 2017-12-11

## Channels

- # adventofcode (129)
- # architecture (10)
- # beginners (163)
- # boot (1)
- # cider (34)
- # cljs-dev (9)
- # clojure (210)
- # clojure-austin (11)
- # clojure-czech (2)
- # clojure-gamedev (1)
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- # clojurescript (87)
- # cursive (12)
- # data-science (6)
- # datomic (13)
- # devcards (4)
- # editors (2)
- # emacs (34)
- # figwheel (6)
- # fulcro (147)
- # graphql (17)
- # lumo (54)
- # off-topic (37)
- # om (11)
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- # random (1)
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- # ring (10)
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- # sfcljs (1)
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- # spacemacs (32)
- # test-check (4)
- # unrepl (84)

@minikomi Nice solution! Your throw may make things more robust, but if the input is valid, I think you should be able to take the three cases `\,`

`\newline`

, and `\!`

and eliminate them, if you take the result-expr for `\,`

and use it instead of the `(throw ...)`

.

yeah, i just had it there to refine my solution.. catch (ha!) the times it went awry.

Instead of trying to say it in words, this variation on your solution works for me: https://gist.github.com/mfikes/57c1b666c30bb5fd98b235df87b5c189

Right, I think you can interpret the problem definition that way. And it seems to be borne out by the input data.

If the suffix is added, there's 8 `3, 4, 1, 5, 17, 31, 73, 47, 23`

as the steps.. but the skip sequence carried over is `4`

?

I've used Clojure for all three years, and I feel like some of the earlier problems are easier to solve in a procedural style, but I feel like functional languages really start to shine after a few days.

Though the hash cracking one from... last year?... was a bit tough... I had to learn more about Java interop to make it fast

I'd love to go through and solve these with different paradigms, hone a sense for what gets easier and what gets harder

@fellshard same here, but right now trying to decide between āprettyā with `reduce`

/`reductions` vs 30x faster with `apply`

`(apply str (map #(format "%02x" %) xored))`

Was pretty happy wit that hexidecimal-string-conversion š

Hi all! @fellshard Indeed, ācodaā is a musical term; It literally means ātailā in Italian. It refers to the bars that come after a repeating part. I donāt know how it popped into my mind, but I like it better than ātailā which can be confusing when destructuring linked lists.

Day 11: https://github.com/orestis/adventofcode/blob/master/clojure/aoc/src/aoc/2017_day11.clj

Today I didnāt have much time to arrive to the solution from first principles; I had to lookup hex grids and how they work.

my solution for today: https://github.com/skazhy/advent/blob/master/src/advent/2017/day11.clj with a handy ascii art on how the coordinates are handled.

In my opinion, todayās challenge lent itself well to one of the most elegant & concise solutions this year so far https://github.com/axelarge/advent-of-code/blob/master/src/advent_of_code/2017/day11.clj

@mikelis.vindavs That is indeed very nice.

Did anyone else get emotional while reading > āItās my child process,ā she says, āheās gotten lost in an infinite grid!ā

https://repl.it/repls/BoldAzureCuscus hereās mine

Day 11: https://github.com/mfikes/advent-of-code/blob/master/src/advent_2017/day_11.cljc

I have to admit without the hint about cube coordinates I would still be thinking right now

Me too. I did some quick research and chose that coordinate system because it makes calculating distance trivial.

I solved it without cube coordinates, by using the simplified versions of de diagonals for north and south. So NE + NW = (1,1) + (1,-1) = (2,0). Calculation is simple after that, similar to using a Z-axis.

nice approach with the input resolving directly to coordinate tuples š:skin-tone-2:

oow, still a defect? wrote the solution in a repl / nightcode at work and pasted it in github in one file. Let me fix that.

There is an interesting perf anomaly with @erwin's `solve-2`

where it runs in 124 ms for me in Clojure *vs.* 15 ms in self-hosted ClojureScript. Hrm.

This was the page I hit for the research I did. It has incredible visualizations of the coordinate systems. https://www.redblobgames.com/grids/hexagons/

I hit that one too and then I tried the q layouts, but had problems calculating the distance

I scrolled down to the Distances section and saw that Cube coordinates has a nice formula.

yeah, thatās the same system as on the photograph, but I was nearly awake then š

https://github.com/bhauman/advent-of-clojure-2016/blob/master/src/advent_of_clojure_2017/day11.clj

ok just finished, I spent some time on paper trying to devine the properties of the system first

oh I see others did this as well, congrats @mikelis.vindavs!!

Interesting. @bhauman's also exhibits that odd perf anomaly where part 2 is much faster in Planck.

Planck starts off at 90 ms but then drops down to 30 ms. My guess (based on some stuff Timothy Baldridge was saying): JavaScriptCore uses a tracing JIT, so after it sees execution, it can compile things to machine code that relies purely on primitives. There is evidently something tracing JITs can do that the Java VM can't do with its current implementation, but I don't fully appreciate what is going on.

Perhaps the day 11 problem happens to be highly amenable to tracing analysis, involving a tight loop of math at its core.

Day 12: > Part 1: some random array walking > Part 2: perhaps the day 12 problem happens to be highly amenable to tracing analysis, involving a tight loop of math at its core. > Determine the time spent after running the algorithm on the output of part 1.

FWIW, my solution also exhibits the odd perf anomaly: `part-2`

is 124 ms in Clojure and 19 ms in Planck / JavaScriptCore.

using the tips and tricks from day5 i see some boxed math and reflection optimization possibilities, so I would say that it is indeed the tracing jit

https://github.com/ekroon/adventofcode2017/commit/95d397e70fb1485a16a0a9ae30a61a0c80117320 adding ^int ^int ^int ... and it is 10ms and 20 ms

Yeah, for me the call to `Math/max`

was using reflection. š± My solution dropped from 124 ms to 8 ms with https://github.com/mfikes/advent-of-code/commit/8b71e9a87f7e9dee970fc6f5176edf30bb2569db#diff-71207370594c4dd13d58690ffbff0646

wasnāt this kind of type hint also valid? `(defn ^long distance [ā¦] ā¦)`

. When I call distance from the REPL it works fine

But when I call it from another form, I get: java.lang.IllegalArgumentException: Unable to resolve classname: [email protected]

@borkdude I think that's where they go in ClojureScript, but in Clojure

```
(defn d ^long [] 1)
```

why canāt I use ^longs here (instead of annotating each element): https://github.com/borkdude/aoc2017/blob/master/src/day11.clj#L28

> What about when you have a sequence of values, all of a uniform type? Clojure provides a number of special hints for these cases, namely ^ints, ^floats, ^longs, and ^doubles. https://github.com/clojure-cookbook/clojure-cookbook/blob/master/08_deployment-and-distribution/8-05_type-hinting.asciidoc

so I think as long as youāre using the entire sequence, the type hint will work, but not for individually destructured elements

This is a bit funny. This give a type hint warning:

```
(defn f [[x y z]]
(+ x y z))
```

but this doesnāt
```
(defn f [[x y z]]
(apply + [x y z]))
```

Ahh, that's cool. By doing `(set! *unchecked-math* :warn-on-boxed)`

you are essentially saying you want the `(+ ...)`

form to use unchecked math (presumably replacing `clojure.core/+`

with `clojure.core/unchecked-add`

in some way at compile time), but it is warning that it can't actually employ unchecked math because the values are boxed as `Object`

instances? (Which can be fixed by type hinting them.)
But in the second form, `+`

is not being compiledāit is being passed in as a higher-order function to `apply`

, so the result is that you get checked arithmetic regardless.

I'd like to know why you can't make the second form use unchecked arithmetic by changing it to:

```
(defn f [[x y z]]
(reduce unchecked-add [x y z]))
```

OK, so

```
(unchecked-add Long/MAX_VALUE Long/MAX_VALUE)
```

but no
```
(apply unchecked-add [Long/MAX_VALUE Long/MAX_VALUE])
```

Also no

```
(let [ua unchecked-add] (ua Long/MAX_VALUE Long/MAX_VALUE))
```

Compiler chicanery.I think this is why Zach wrote https://github.com/ztellman/primitive-math

I like Zach's intro here https://groups.google.com/forum/#!msg/clojure/d89gjX_5Om8/KgBcIORMGYYJ

I finished an alternate solution for day11 that doesn't use a coordinate system https://github.com/thegeez/clj-advent-of-code-2017/blob/master/src/advent/day11.clj#L166

`replacement-moves`

turns two moves into either zero, one or two moves. For instance [:n :s] is the same as doing nothing, [:n :se] is the same as take a single :se step
one by one the steps from moves are added to the shortest path, where the added step might undo a previous step, combine with another step into a single step or the step is added