[L.slice(0,i), L.slice(i)] creative solution for Split List by danielsan - javascript coding challenges

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[L.slice(0,i), L.slice(i)] solution in Creative category for Split List by danielsan

var splitList = (L: number[], i=(L.length/2+.5|0)) => [L.slice(0,i), L.slice(i)]

April 25, 2020

Comments:

Dmitry_Sternyaev_69ebf6f25e8e4 on May 15, 2020, 1:54 p.m.
Wow

hbxz on May 21, 2020, 10:48 a.m.
oh. what is `+.5|0` magic

vincent.tscherter on June 3, 2020, 9:43 a.m.
this is a Bitwise OR, cf. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators#Bitwise_OR">Bitwise Operators</a>

danielsan on June 3, 2020, 4:14 p.m.
Hi @hbxz, the bitwise OR is used here with a different intention of its original purpose. Originally it is meant to be used to look at each bit of a sequence of bits, like a byte for instance, and compare position by position with another sequence of bits. Example: ```js 0100 = 4 in binary | 0101 = 5 in binary | 100 = 4 in binary | 101 = 5 in binary | 1000 = 8 in binary | 1001 = 9 in binary | 000 = 0 in binary | 000 = 0 in binary | ---- | ---- | ---- | ---- | 1100 = 12 in binary | 1103 = 13 in binary | 100 = 4 in binary | 101 = 5 in binary | ``` If there's a 1 in either side it will result in 1 So, if you run ```9 | 5``` or ```5 | 9``` the result is ```13``` But these operators only work for integers, they discard anything after the decimal point, and since these operations are extremely fast and, as you can see above, any bitwise or with 0 will return exactly the same as the other number, using ```x|0``` is a very fast way to achieve the same as <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/floor">Math.floor</a>, which rounds a number down to the nearest integer. So the reason I'm using that is because of its side-effects not because of its original intent.

vincent.tscherter on June 2, 2020, 1:31 p.m.
what about <pre class='brush: javascript'>var splitList = v => [ v.splice(0, (v.length+1)>>1), v] </pre> no additional var needed

danielsan on June 3, 2020, 3:54 p.m.
One has to choose what one is looking for. Although your solution returns a similar value it is saving 1 variable allocation at the cost of using a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice">slower operation</a> that also mutates the original input, which is a bad practice. So in the battle of ```1 extra variable``` with <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice">slice</a> vs ```slower code with side effects``` with <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice">splice</a> I'd still pick the first.

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