JavaScript Program for array rotation

Array rotation in JavaScript involves shifting elements within an array to the left or right by a specified number of positions.

There are several approaches to rotate an array in JavaScript which are as follows:

Using Array Slice and Concatenation Method

This approach involves slicing the array into two parts based on the rotation index and then concatenating them in the desired order. This method first calculates the rotation index, then slices the array accordingly, and concatenates the parts in the rotated order.

Syntax:

  // Create the rotated array by concatenating two slices
    const rotatedArray = arr.slice(rotateBy).concat(arr.slice(0, rotateBy));
    
  // Return the rotated array
    return rotatedArray;

Example: TypeScript Array Rotation: Left Rotate by 2 Positions - Demonstrating a function to rotate an array leftward by a specified number of positions.

function rotateArray(arr, rotateBy) {
    const n = arr.length;
    rotateBy %= n;

    return arr.slice(rotateBy).concat(arr.slice(0, rotateBy));
}

const originalArray = [1, 2, 3, 4, 5];
const rotatedArray = rotateArray(originalArray, 2);
console.log(rotatedArray); 

[ 3, 4, 5, 1, 2 ]

Using the Array Splice and Push method

This approach involves using the splice() method to remove elements from the beginning of the array and then push them to the end. Here, we first remove the elements to be rotated from the beginning of the array using splice() and then push them to the end using the spread operator (...).

Example: TypeScript In-Place Array Rotation: Left Rotate by 2 Positions - Demonstrating a function for in-place left rotation of an array by a specified number of positions.

function rotateArray(arr, rotateBy) {
    const n = arr.length;
    rotateBy %= n;

    arr.push(...arr.splice(0, rotateBy));
    return arr;
}

const originalArray = [1, 2, 3, 4, 5];
const rotatedArray = rotateArray(originalArray, 2);
console.log(rotatedArray);

[ 3, 4, 5, 1, 2 ]

Using Array Reversal

This approach involves three steps first reversing the first part of the array, reversing the second part, and then reversing the whole array. This method needs a helper function reverse() to reverse elements within specified ranges and allow us to perform array rotation efficiently.

Example: TypeScript Array Rotation: Left Rotate by 2 Positions - Utilizing Reversal Algorithm - Demonstrating an efficient in-place left rotation algorithm for arrays using reversal.

function rotateArray(arr, rotateBy) {
    const n = arr.length;
    rotateBy %= n;

    reverse(arr, 0, rotateBy - 1);
    reverse(arr, rotateBy, n - 1);
    reverse(arr, 0, n - 1);

    return arr;
}

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

const originalArray = [1, 2, 3, 4, 5];
const rotatedArray = rotateArray(originalArray, 2);
console.log(rotatedArray);

[ 3, 4, 5, 1, 2 ]