[SPOILER ALERT] Advent of Code 2022: Day 3 solutions

[Junilu Lacar]

SPOILER ALERT This thread contains solution code for Day 3 of Advent of Code 2022.






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SPOILER ALERT This thread contains solution code for Day 3 of Advent of Code 2022.

[Junilu Lacar]

Here's my Day 3 solution in Kotlin: https://github.com/jlacar/adventofcode2022-kotlin/blob/main/untitled/src/main/kotlin/Day3.kt

I just remembered that Kotlin had a way to chunk streams. Will try that as an alternate solution.

Edit: Yup, significantly reduced lines of code by using chunked(3) - very nice, if I say so myself.

[Junilu Lacar]

Every refactoring leads to another. This goes back to what I was telling someone just the other day: if you refactor for clarity, you begin to see deeper patterns in the code that give you opportunities to refactor further.

I see that my most recent refactoring has revealed a pattern that I can use to tighten the code up to generalize the algorithm.

[Liutauras Vilda]

My solutions probably aren't readable for non racketeers, but I'm not sure racket is readable in general.

(define input (map (λ (e) (string->list e)) (file->lines "input/day03.txt")))

(define priority (λ (e) (- (char->integer e) (if (char-lower-case? e) 96 38))))

(apply + (map priority
              (map (λ (e) (car (set-intersect (car e) (cadr e))))
                   (map (λ (e) (list (take e (/ (length e) 2)) (drop e (/ (length e) 2)))) input))))

(define (intersect-slice l result)
  (cond [(empty? l) result]
        [(> (length l) 3) (intersect-slice (cdddr l) (append (set-intersect (car l) (cadr l) (caddr l)) result))]
        [else (intersect-slice '() (append (set-intersect (car l) (cadr l) (caddr l)) result))]))
                    
(apply + (map priority (intersect-slice input '())))

I shall try moving forward to decompose solution by giving lambdas some meaningful names, so the solution could be told in declarative sentence.

[Junilu Lacar]

Liutauras Vilda wrote:My solutions probably aren't readable for non racketeers, but I'm not sure racket is readable in general.

Well, if we put them side by side...

Racket
(define priority (λ (e) (- (char->integer e) (if (char-lower-case? e) 96 38))))
Kotlin

fun priority(ch: Char) = 
   ch.lowercaseChar() - 'a' + (if (ch.isLowerCase()) 1 else 27)

Java

int priority(ch: char) {
   return Character.toLowerCase(ch) - 'a' + (Character.isLowerCase(ch) ? 1 : 27);
}

I'm just wondering how you came up with 96 and 38. I could imagine defining these constants:

private const val PRIORITY_lower_a = 1;
private const val PRIORITY_UPPER_A = 27;

But what names would 96 and 38 get to make them more readable?

[Junilu Lacar]

Junilu Lacar wrote:I could imagine defining these constants:

private const val PRIORITY_lower_a = 1;
private const val PRIORITY_UPPER_A = 27;

With those constants, I'd refactor to this:

fun priority(ch: Char) =
   if (ch.isLowerCase()) PRIORITY_lower_a else PRIORITY_UPPER_A
   + ch.lowercaseChar() - 'a'

Edit: I guess not. Apparently, I have to keep it like this:

fun priority(ch: Char) = ch.lowercaseChar() - 'a' +
    if (ch.isLowerCase()) PRIORITY_lower_a else PRIORITY_UPPER_A