Rotate an Array to the Right by K Steps using JavaScript

One can Rotate an array to the left by k steps using JavaScript. We are given an input array and a value k we have to rotate that array by k steps in the right direction.

Example:

Input 
arr = [1 , 2 , 3 , 4 , 5 ]
k = 3 

Output 
arr = [ 3 , 4 , 5 , 1 , 2]

Below are different approaches to Rotate an array to the left by k steps using JavaScript which are as follows:

Using Reverse Method

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array. Now Reverse the entire array. Reverse the first k elements of the array, where k is number of steps we have to rotate array in right direction. Reverse the remaining elements of the array. Return modified array.

Example: To demonstrate Rotation of an array to the left by k steps using reverse method only

JavaScript

function rotateArrayReverse(nums, k) {
    const n = nums.length;
    k = k % n;


    // Reverse the entire array
    nums.reverse();

    // Reverse the first k elements
    reverseArray(nums, 0, k - 1);

    // Reverse the remaining elements
    reverseArray(nums, k, n - 1);

    return nums;
}


function reverseArray(arr, start, end) {
    while (start < end) {
        const temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        start++;
        end--;
    }
}

const nums = [1, 2, 3, 4, 5, 6, 7];
const k = 3;
console.log(rotateArrayReverse(nums, k)); 

Output

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

Time complexity : O(n)

Space complexity : O(1)

Using Array Splice and Push

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array. Now Use the splice method to remove the last k elements from the array and Push the removed elements at the beginning of the array. Return the modified array.

Example: To demonstrate Rotation of an array to the left by k steps using array splice and push

JavaScript

function rotateArraySplice(nums, k) {
    const n = nums.length;
    k = k % n; 

    // Remove the last k 
    // elements from  array
    const removed = nums.splice(-k);

    // Insert the removed elements
    // at starting of the array
    nums.unshift(...removed);

    return nums;
}


const nums = [1, 2, 3, 4, 5, 6, 7];
const k = 3;
console.log(rotateArraySplice(nums, k)); 

Output

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

Time complexity : O(k)

Space complexity : O(k)

Using Slice and Concatenation

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array. Now Use the slice() method to extract the last k elements and the remaining elements of the array. Concatenate the sliced parts: Concatenate the sliced parts in reverse order using the concat() method. Return the modified array

Example : To demonstrate Rotation of an array to the right by k steps using array splice and push

JavaScript

function rotateArraySliceConcat(nums, k) {
    const n = nums.length;
    k %= n; 

    // Concatenate the sliced parts in reverse order
    const rotated = nums.slice(-k).concat(nums.slice(0, n - k));

    return rotated;
}


const nums = [1, 2, 3, 4, 5, 6, 7];
const k = 3;
console.log(rotateArraySliceConcat(nums, k)); 

Output

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

Time Complexity: O(k + m)

Space Complexity: O(k + m)