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Discussion on: Daily Coding Puzzles - Nov 4th - Nov 9th

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aspittel profile image
Ali Spittel Author

Wednesday

Array.diff (6 KYU):

Your goal in this kata is to implement a difference function, which subtracts one list from another and returns the result.

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Tyler James Leonhardt • Edited

PowerShell

$a | ? { $_ -notin $b }

Expanding the ? alias:

$a = @(1,2,3,4)
$b = @(2,3,4,5)

$a | Where-Object { $_ -notin $b }
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Jermaine Oppong

Here's one in Dart:

arrayDiff(List a, List b) => a..retainWhere((i) => !b.contains(i));
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dance2die profile image
Sung M. Kim • Edited

It wasn't as easy as doing a set difference as the a needed to keep the duplicate values.

Below is the answer in C#.

Where is the same as filter in JavaScript.

using System.Linq;
using System.Collections.Generic;

public class Kata
{
  public static int[] ArrayDiff(int[] a, int[] b)
  {
    var hash = new HashSet<int>(b);
    return a.Where(_ => !hash.Contains(_)).ToArray();
  }
}
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Ben Berbass

PHP

array_diff(a, b);
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ben profile image
Ben Halpern

Ruby

a - b
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gartboy profile image
Garrett

Similar effort when done in APL! :)

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aspittel profile image
Ali Spittel Author

That's amazing!

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ben profile image
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ben profile image
Ben Halpern

On the other hand, Ruby probably allocated about 10,000 object references under the hood and used 1gb of memory to make that happen. 😄

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thejessleigh profile image
jess unrein • Edited

Honestly, I just came out here to have a good time and I'm feeling so attacked right now 😅😅😅

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ben profile image
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thejessleigh profile image
jess unrein

Haha nice. Honestly, I'm just so used to copy/pasting emojis from slack and discord. Fun fact, when you do that, it copies the colon emoji syntax, not the unicode glyph 😅🙃

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Ricardo Tomasi

@bendhalpern some numbers (using /usr/bin/time -l on OSX):

Go: 0.0s, 1.5Mb
Go run: 0.10s, 24Mb
Node: 0.06s, 19Mb
Ruby: 0.08s, 11Mb
Crystal: 0.0s, 1.5Mb
Crystal run: 0.4s, 10.4Mb
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rakenodiax
Rust: 0.00s - 1.12MiB
Rust (nightly): 0.01s - 0.88MiB
Go: 0.00s - 1.64MiB
Go run: 0.25s - 24.11MiB
Python: 0.21s - 5.48MiB

Disclaimer: I'm inexperienced with Go; using the example from below 😅

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thejessleigh profile image
jess unrein

Oh, I know almost nothing about Go. I'm specifically using these exercises to learn the syntax. No clue if and how what I'm doing can be optimized. Go is famously, weirdly restrictive and intentionally verbose.

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Anologicon

kkkkk it's very simple dude :D

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Sung M. Kim

Ah, cannot unsee this answer... 😆

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Roman Elizarov

Same in Kotlin :)

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Mateus Vahl

Hey all, Why I don't see any java code here?

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Kasey Speakman

F#

let diff a b =
    a |> Array.filter (fun v -> not (b |> Array.contains v))

also sequence expression syntax

let diff a b =
    [|
        for value in a do
            if not (b |> Array.contains value) then
                yield value
    |]
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t4rzsan profile image
Jakob Christensen

Or (although it will also remove duplicates from a):

(a |> Set.ofSeq) - (b |> Set.ofSeq)
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kspeakman profile image
Kasey Speakman

Yes, this was my first thought, but I was trying to retain dupes.

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Christopher McClellan

Just define the subtraction operator and done.

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aspittel profile image
Ali Spittel Author • Edited

Python!

def array_diff(a, b):
    return [l for l in a if l not in b]
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thejessleigh profile image
jess unrein

List comprehensions are truly a gift.

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aspittel profile image
Ali Spittel Author

YES -- they are so elegant.

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Daniel Schep

Or with sets!

def array_diff(a, b):
    return list(set(a) - set(b))
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David Wickes • Edited

Common Lisp

I'll use lists because... well, it's Lisp, right?

(set-difference '(1 2 2 2 3) '(2))
;; => (3 1)

Can't beat a good standard library ;)

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Garrett

APL

 a ~ b 

Replied to the post instead of the comment! My bad!

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Sebastian Martin Dicke

Haskell

array_diff :: Eq a => [a] -> [a] -> [a] 
array_diff a b = filter (\x -> notElem x b) a
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Sebastian Martin Dicke • Edited

Another Haskell solution:

array_diff :: Eq a => [a] -> [a] -> [a]
array_diff a b = [x | x <- a, x `notElem` b]
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clandau profile image
Courtney
function array_diff(a, b) {
  let counter = {};
  for(let i of b) {
    counter[i] = true;
  }
  let result = a.filter(item => counter[item] !== true);
  return result;
}
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jess unrein

Go

func Difference(a []int, b []int) (diff []int) {
    m := make(map[int]bool)

    for _, item := range b {
        m[item] = true
    }

    for _, item := range a {
        if _, presence := m[item]; !presence {
            diff = append(diff, item)
        }
    }
    return
}
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Jay

Rust

  • With Liftime. The returned Vec<&T> has elements borrowed and valid until the list1 is valid.
fn diff<'a, T>(list1: &'a [T], list2: &[T]) -> Vec<&'a T>
where
    T: PartialEq,
{
    list1.into_iter().filter(|e| !list2.contains(e)).collect()
}
  • Without lifetime We return a new Vec free from any list provided, by cloning the data. The generic data type only allows the data type that implements Clone trait to be passed.
fn diff2<T>(list1: &[T], list2: &[T]) -> Vec<T>
where
    T: PartialEq + Clone,
{
    list1
        .into_iter()
        .map(|x| x.clone())
        .filter(|e| !list2.contains(&e))
        .collect()
}
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Paul Susicky

Tried in Javascript

function arrayDiff(arr1, arr2) {
    return arr1.filter(val => !arr2.includes(val));
}
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aspittel profile image
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Neocortexxx

Wow, great! So clean!