Move array to the right, and make missing space 0

Question

I am trying to move an array to the right by a set value, and replacing the now missing spaces with 0. I just can not figure out how to do it.

Array before moving:

let array = [1,2,3,4,5,6,7]

Array after moving 2 to the right:

array = [0,0,1,2,3,4,5]

Ive looked at other stack overflow posts but those just wrap around the data making a move to the right look like this:

array = [6,7,1,2,3,4,5]

Whilst I want to just remove the 6 and 7.

Please show what research you've done and what attempts you've made based on that research. — Heretic Monkey, Oct 23 '20 at 21:56
No, Im not looking to add new data just shift everything to the right and replace the gap with 0. — Samo2120, Oct 23 '20 at 22:00
It does provide part of the answer to your question if you'd just apply yourself a bit — Dexygen, Oct 23 '20 at 22:01
@Samo2120 You *are* looking to add new data. The new data is `0`. Just do it in a loop `n` times. — Barmar, Oct 23 '20 at 22:02
No because the array isn't fixed, in the example it just makes the array longer, Im looking to keep it the same length — Samo2120, Oct 23 '20 at 22:03
@Barmar A loop? Seriously? For somebody who's rep on here is so high that is an egregiously horrible suggestion. — Dexygen, Oct 23 '20 at 22:04
And you can keep it the same length, IF YOU'D ONLY JUST APPLY YOURSELF — Dexygen, Oct 23 '20 at 22:05
@Dexygen Unless you're inserting hundreds or thousands, the O(n^2) complexity is not a big deal. — Barmar, Oct 23 '20 at 22:05
Just `unshift` with 0's and the `pop` off the last numbers, and do that in a loop, O(n^1) — Samathingamajig, Oct 23 '20 at 22:06

score 2 · Accepted Answer · answered Oct 23 '20 at 22:07

Just unshift with 0's and the pop off the last numbers.

function shiftArray(arr, numberOf0s) {
  for (let i = 0; i < numberOf0s; i++) {
    arr.unshift(0);
    arr.pop();
  }
}

function shiftArray(arr, numberOf0s) {
  for (let i = 0; i < numberOf0s; i++) {
    arr.unshift(0);
    arr.pop();
  }
  return arr;
}

let array = [1,2,3,4,5,6,7];

console.log(array);

shiftArray(array, 2);

console.log(array);

Sash Sinha · Answer 2 · 2020-10-23T22:28:19.840

As with most languages manipulating an array type data structure anywhere other than the back via methods like insert, unshift is not ideal. This is because of the way elements of an array are stored in memory i.e., contiguously. For this reason, each insert or unshift operation requires moving all the elements after it every time to maintain this "contiguousness". Basically, you should avoid using these methods unless you absolutely have to when working with arrays.

Luckily in this case you can just iterate over the array in reverse and copy the element to its correct position and fill in the remaining slots with zeros for an O(n) solution where n is the length of the array:

const moveToRight = (array, n) => {
    if (array === undefined || array.length == 0) {
        return;
    }
    if (n < 0) {
        throw 'Error n cannot be negative!';
    }
    let i = array.length - 1;
    while (i >= 0 + n) {
        array[i] = array[i - n];
        i--;
    }
    while (i >= 0) {
        array[i] = 0;
        i--;
    }
    return;
}

array = [1, 2, 3, 4, 5, 6, 7];
try {
    moveToRight(array, 2);
} catch (e) {
    console.error(e);
}
console.log(array);

Move array to the right, and make missing space 0

2 Answers2