Rotate Array

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Lesson

Given an array of

elements and an integer

, write a function called

rotateArray

that rotates the array

steps to the right. For example, given the array

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

and

k = 3

, the output should be

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

Consider how you might implement this by just using Array builtin methods as well as traditional loops.

Traditional Looping Solution

Another way to solve the problem "Rotate Array" is to use a while loop along with splice()
and unshift()
methods. In this approach, we use a while loop to repeatedly remove the last element of the array using the splice method and then add it to the beginning of the array using the unshift method. Here is an example of this solution in code:

function rotateArray(arr, k) {
    while (k > 0) {
        // remove last element of the array
        let removedElement = arr.splice(-1, 1);
        // add removed element to the beginning of the array
        arr.unshift(removedElement[0]);
        k--;
    }
    return arr;
}

Video Solution:

Using Array Builtins

Use the splice()
method to remove the last k elements of the array, and then use the unshift()
method to add them to the beginning of the array.

Here's an example of this solution in code:

function rotateArray(arr, k) {
    // remove the last k elements of the array
    let removedElements = arr.splice(-k, k);
    // add the removed elements to the beginning of the array
    Array.prototype.unshift.apply(arr, removedElements);
    return arr;
}

Notice the use of

Array.prototype.unshift.apply(arr, removedElements);

rather than

arr.unshift(removedElements);

arr.unshift(removedElements)
would add the entire removedElements
array as a single element to the beginning of the arr
array, resulting in an array that looks like [[5,6,7], 1,2,3,4]
.
Array.prototype.unshift.apply(arr, removedElements)
on the other hand, uses the apply()
method to apply the unshift()
method to the arr
array, and pass the removedElements
array as separate arguments. This allows each element of the removedElements
array to be added individually to the beginning of the arr
array, resulting in an array that looks like [5,6,7,1,2,3,4]
.In other words, arr.unshift(removedElements)
will add the removedElements
array as a single element to the arr
array, while Array.prototype.unshift.apply(arr, removedElements)
will add each element of the removedElements
array individually to the arr
array.

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