# Insert into array in reverse while iterating forward

So currently I have this function:

function loadPath(chunkSize, dataSize, depth, index) {
let path = []
let i = 0
while (i < depth) {
path.unshift(index % chunkSize)
index = Math.floor(index / chunkSize)
i++
}
return path
}


I would now like to pass in path as a variable from an object pool of short path arrays. So for example:

function loadPath(path, chunkSize, dataSize, depth, index) {

}

let path = new Array(3)
console.log(path) // 1, 3, 1
console.log(path) // ...


The question is, how can I do that without using push/unshift or reverse operations on the array? Basically just treating the array as a static block of memory, while at the same time not adding any unnecessary operations.

function loadPath(path, chunkSize, dataSize, depth, index) {
let i = 0
let x = depth - 1
while (i < depth) {
path[x] = index % chunkSize
index = Math.floor(index / chunkSize)
i++
x--
}
}


My question is, can this be done with any fewer temp variables? Some magic along the lines of this?

function loadPath(path, chunkSize, dataSize, depth, index) {
let i = 0
while (i < depth) {
// something tricky perhaps here?
// since x and i have a reciprocal relationship...
// somehow fill it in backwards...
path[depth - i] = index % chunkSize
index = Math.floor(index / chunkSize)
i++
}
}


Or perhaps there is another way entirely to write this algorithm to be in as few steps and operations and temp variables as possible.

Could also use this floor implementation integrated somehow if it helps :)

function floor(n) {
return ~~n - (~~n > n)
}

• Your title short be short and concise while explaining what your code does. – FreezePhoenix Sep 25 '20 at 12:19
• You should be able to calculate the number of loops you need to do, so you can create an empty array of that size and fill it backwards. If I'm not mistaken it should be Math.log(chunkSize) / Math.log(index) (rounded up). – RoToRa Sep 25 '20 at 13:44
• Would you consider using concat? – iAmOren Sep 25 '20 at 14:08
• How about: path[depth - i - 1] = index % chunkSize - no need for x. – iAmOren Sep 25 '20 at 14:18
• What is this mysterious index and what is/why are you not using dataSize? – iAmOren Sep 25 '20 at 14:20

Let's try the other way:

function loadPath(path, chunkSize, dataSize, depth, index) {
for(var i = 0; i < depth; i++) {
path[depth - i - 1] = index % chunkSize;
index = Math.floor(index / chunkSize);
};
};

var path = Array(3);
console.log(path);
console.log(path);
.as-console-wrapper { max-height: 100% !important; top: 0; }

What do you want to do if index >= chunkSize^3?

• Thank you for the accept! Up-vote, please?!? :) Still: What do you want to do if index >= chunkSize^3? – iAmOren Sep 25 '20 at 21:50
• I can handle that outside of the function no problem. – Lance Pollard Sep 25 '20 at 22:03
• Great! Thanks for the up-vote. I still have no clue as to what you are doing... :) – iAmOren Sep 25 '20 at 22:06
• I am working on a vm and this is an aspect of the memory allocation part. – Lance Pollard Sep 25 '20 at 22:17
• Without a declaration for i using var or let a global variable would be created, which won't lead to an error but typically frowned upon – Sᴀᴍ Onᴇᴌᴀ Sep 26 '20 at 11:03

Hint: accept and up-vote both... :)

function recBucket(number, size) {
if(number<size) return [number];
else {
var whole=Math.floor(number/size);
return [recBucket(whole, size), number-whole*size].flat();
}
};

function loadPath(chunkSize, dataSize, depth, index) {
return recBucket(index, chunkSize);
};

console.log(loadPath(5, 100, 3, 50));
.as-console-wrapper { max-height: 100% !important; top: 0; }
• .flat feels a feels a bit hacky, just hiding implementation details to make things appear shorter. – Lance Pollard Sep 25 '20 at 16:04