Array Rotation Techniques in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to rotate the array to the right by one position.

DSA Typescript

function rotateRightByOne(arr: number[]): number[] {
  const last = arr[arr.length [1] 1];
  for (let i = arr.length - 1; i > 0; i--) {
    arr[i] = arr[i - 1];
  }
  arr[0] = last;
  return arr;
}

Drag options to blanks, or click blank then click option'

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of - causes out-of-bound error.

Using * or / is incorrect for indexing.

We subtract 1 from the array length to get the last index.

2fill in blank

medium

Complete the code to rotate the array to the left by one position.

DSA Typescript

function rotateLeftByOne(arr: number[]): number[] {
  const first = arr[0];
  for (let i = 0; i < arr.length - 1; i++) {
    arr[i] = arr[i [1] 1];
  }
  arr[arr.length - 1] = first;
  return arr;
}

Drag options to blanks, or click blank then click option'

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using - instead of + causes wrong indexing.

Using * or / is invalid for array indices.

We add 1 to move each element to the left.

3fill in blank

hard

Fix the error in the code to rotate the array right by k positions using reversal.

DSA Typescript

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

function rotateRightByK(arr: number[], k: number): number[] {
  k = k [1] arr.length;
  reverse(arr, 0, arr.length - 1);
  reverse(arr, 0, k - 1);
  reverse(arr, k, arr.length - 1);
  return arr;
}

Drag options to blanks, or click blank then click option'

A/

B%

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using division or multiplication instead of modulo.

Not adjusting k when it exceeds array length.

We use modulo to handle cases where k is larger than array length.

4fill in blank

hard

Fill both blanks to create a function that rotates the array left by k positions using slicing.

DSA Typescript

function rotateLeftByK(arr: number[], k: number): number[] {
  k = k [1] arr.length;
  return arr.slice(k).[2](arr.slice(0, k));
}

Drag options to blanks, or click blank then click option'

A%

Bconcat

Cpush

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using push or pop instead of concat.

Not using modulo for k.

Modulo ensures k is within bounds, and concat joins the two slices.

5fill in blank

hard

Fill all three blanks to implement a function that rotates the array right by k positions using unshift and pop.

DSA Typescript

function rotateRightByKUsingPop(arr: number[], k: number): number[] {
  k = k [1] arr.length;
  for (let i = 0; i < k; i++) {
    const last = arr.[2]();
    arr.[3](last);
  }
  return arr;
}

Drag options to blanks, or click blank then click option'

A%

Bpop

Cunshift

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift instead of pop.

Using push instead of unshift.

Not using modulo for k.

Modulo keeps k valid, pop removes last element, unshift adds it to front.

Practice

1. What does rotating an array to the right by 1 position mean?
Example: [1, 2, 3, 4] rotated right by 1 becomes?

easy

A. [4, 1, 2, 3]

B. [2, 3, 4, 1]

C. [1, 2, 3, 4]

D. [3, 4, 1, 2]

Solution

1. Step 1: Understand right rotation

   Right rotation by 1 means the last element moves to the front, shifting others right.

2. Step 2: Apply to example array

   Last element 4 moves to front, rest shift right: [4, 1, 2, 3].

3. Final Answer:

   [4, 1, 2, 3] -> Option A

4. Quick Check:

   Right rotate by 1 = last element front [OK]

Hint: Right rotate by 1 means last element moves front [OK]

Common Mistakes:

• Confusing right rotation with left rotation
• Not moving the last element to front
• Shifting elements incorrectly

2. Which of the following TypeScript code snippets correctly rotates an array arr to the left by 1 position?

easy

A. arr.push(arr.shift()!)

B. arr.unshift(arr.pop()!)

C. arr.pop(); arr.unshift(arr.pop()!)

D. arr.shift(); arr.push(arr.shift()!)

Solution

1. Step 1: Understand left rotation by 1

   Left rotation by 1 means first element moves to the end.

2. Step 2: Check code snippets

   arr.push(arr.shift()!) uses arr.shift() to remove first element and arr.push() to add it at end, correct for left rotation.

3. Final Answer:

   arr.push(arr.shift()!) -> Option A

4. Quick Check:

   Left rotate = shift then push [OK]

Hint: Left rotate by 1 = remove first, add to end [OK]

Common Mistakes:

• Using pop instead of shift for left rotation
• Using unshift with pop for left rotation
• Calling shift or pop twice incorrectly

3. What is the output of the following TypeScript code?

const arr = [10, 20, 30, 40, 50];
const k = 2;
const rotated = arr.slice(-k).concat(arr.slice(0, arr.length - k));
console.log(rotated);

medium

A. [50, 10, 20, 30, 40]

B. [40, 50, 10, 20, 30]

C. [20, 30, 40, 50, 10]

D. [30, 40, 50, 10, 20]

Solution

1. Step 1: Understand slicing for rotation

   arr.slice(-k) takes last 2 elements: [40, 50]. arr.slice(0, arr.length - k) takes first 3 elements: [10, 20, 30].

2. Step 2: Concatenate slices

   Concatenating gives [40, 50, 10, 20, 30], which is right rotation by 2.

3. Final Answer:

   [40, 50, 10, 20, 30] -> Option B

4. Quick Check:

   Right rotate by 2 = last 2 front [OK]

Hint: Right rotate by k = last k elements + rest [OK]

Common Mistakes:

• Using slice with wrong indices
• Confusing left and right rotation
• Not concatenating slices in correct order

4. Find the error in this TypeScript function that rotates an array to the left by k positions:

function rotateLeft(arr: number[], k: number): number[] {
  for (let i = 0; i < k; i++) {
    arr.push(arr.shift());
  }
  return arr;
}

medium

A. arr.push() should be arr.unshift()

B. Loop should run from i = 1 to k

C. arr.shift() can return undefined, causing push(undefined)

D. Function should return void, not number[]

Solution

1. Step 1: Check arr.shift() return type

   arr.shift() returns element or undefined if array empty. Here, no check for undefined.

2. Step 2: Effect on arr.push()

   If arr.shift() returns undefined, arr.push(undefined) adds undefined to array, causing incorrect result or runtime issues.

3. Final Answer:

   arr.shift() can return undefined, causing push(undefined) -> Option C

4. Quick Check:

   shift may be undefined, must check [OK]

Hint: Check shift() return before push to avoid undefined [OK]

Common Mistakes:

• Ignoring undefined from shift()
• Wrong loop range assumptions
• Confusing push and unshift methods

5. Given an array arr of length n, how can you rotate it to the left by k positions efficiently without using extra space? Choose the correct approach.

hard

A. Use a temporary array to store first k elements, then shift rest left, then copy temp at end

B. Sort the array and then rotate by k positions

C. Rotate one by one k times using shift and push

D. Reverse first k elements, reverse last n-k elements, then reverse whole array

Solution

1. Step 1: Understand in-place rotation using reversal

   Reversing parts of array and then whole array rotates left by k without extra space.

2. Step 2: Apply reversal steps

   Reverse first k elements, reverse last n-k elements, then reverse entire array to get rotated array.

3. Final Answer:

   Reverse first k, reverse last n-k, reverse whole array -> Option D

4. Quick Check:

   Reversal method = in-place left rotate [OK]

Hint: Use triple reversal for in-place left rotation [OK]

Common Mistakes:

• Using extra array when not needed
• Rotating one by one causing O(n*k) time
• Sorting array unrelated to rotation