Array Insertion at Middle Index in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert an element at the middle index of the array.

DSA Typescript

const arr = [1, 2, 4, 5];
const middle = Math.floor(arr.length / 2);
arr.splice([1], 0, 3);
console.log(arr);

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

A0

Barr.length

Cmiddle

Darr.length - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 inserts at the start, not the middle.

Using arr.length inserts at the end, not the middle.

The splice method inserts elements at the specified index. Using middle inserts the element at the middle of the array.

2fill in blank

medium

Complete the code to find the middle index correctly for an odd-length array.

DSA Typescript

const arr = [10, 20, 30, 40, 50];
const middle = [1];
console.log(middle);

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

AMath.floor(arr.length / 2)

BMath.ceil(arr.length / 2)

Carr.length / 2

Darr.length - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using Math.ceil which gives an index beyond the middle.

Using arr.length - 1 which is the last index.

Using Math.floor(arr.length / 2) gives the correct middle index for odd-length arrays.

3fill in blank

hard

Fix the error in the code to insert element 99 at the middle index.

DSA Typescript

const arr = [5, 10, 15, 20];
const mid = Math.floor(arr.length / 2);
arr.splice(mid, [1], 99);
console.log(arr);

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

A0

B2

C1

Darr.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 deletes the element at the middle index.

Using arr.length removes too many elements.

The second argument to splice is the number of elements to remove. To insert without removing, use 0.

4fill in blank

hard

Fill both blanks to insert element 7 at the middle index without removing any elements.

DSA Typescript

const arr = [2, 4, 6, 8];
const mid = [1];
arr.splice(mid, [2], 7);
console.log(arr);

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

AMath.floor(arr.length / 2)

B1

C0

Darr.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as delete count removes an element.

Using arr.length as index inserts at the end.

Calculate the middle index with Math.floor(arr.length / 2) and set delete count to 0 to insert without removing.

5fill in blank

hard

Fill all three blanks to insert element 100 at the middle index of the array.

DSA Typescript

const arr = [10, 20, 30, 40, 50, 60];
const mid = [1];
arr.splice(mid, [2], [3]);
console.log(arr);

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

AMath.floor(arr.length / 2)

B0

C100

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete count 1 removes an element.

Inserting at wrong index changes array order.

Calculate middle index with Math.floor(arr.length / 2), delete 0 elements, and insert 100.

Practice

1. What does inserting an element at the middle index of an array mean?

easy

A. Adding the element exactly in the center position of the array

B. Adding the element at the start of the array

C. Adding the element at the end of the array

D. Replacing the middle element with a new element

Solution

1. Step 1: Understand array indexing

   Arrays have positions starting from 0 to length-1. The middle index is usually length/2 (rounded down).

2. Step 2: Define insertion at middle

   Inserting at middle means placing the new element at this middle index, shifting elements after it to the right.

3. Final Answer:

   Adding the element exactly in the center position of the array -> Option A

4. Quick Check:

   Middle insertion = center position [OK]

Hint: Middle index = array length divided by 2 [OK]

Common Mistakes:

• Confusing insertion with replacement
• Inserting at start or end instead of middle
• Not shifting elements after insertion

2. Which of the following TypeScript code snippets correctly inserts the value 99 at the middle index of array arr?

easy

A. arr.unshift(99);

B. arr.push(99);

C. arr.splice(Math.floor(arr.length / 2), 0, 99);

D. arr[ Math.floor(arr.length / 2) ] = 99;

Solution

1. Step 1: Understand splice method

   splice(index, 0, value) inserts value at index without removing elements.

2. Step 2: Check other options

   push adds at end, unshift adds at start, direct assignment replaces element.

3. Final Answer:

   arr.splice(Math.floor(arr.length / 2), 0, 99); -> Option C

4. Quick Check:

   splice with 0 delete count inserts [OK]

Hint: Use splice(index, 0, value) to insert without removal [OK]

Common Mistakes:

• Using push or unshift instead of splice
• Replacing element instead of inserting
• Incorrect index calculation

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

const arr = [10, 20, 30, 40];
arr.splice(Math.floor(arr.length / 2), 0, 25);
console.log(arr);

medium

A. [10, 20, 30, 25, 40]

B. [10, 20, 25, 30, 40]

C. [10, 25, 20, 30, 40]

D. [25, 10, 20, 30, 40]

Solution

1. Step 1: Calculate middle index

   arr.length = 4, middle index = Math.floor(4/2) = 2.

2. Step 2: Insert 25 at index 2

   splice(2, 0, 25) inserts 25 before element at index 2 (which is 30), shifting elements right.

3. Final Answer:

   [10, 20, 25, 30, 40] -> Option B

4. Quick Check:

   Inserted 25 at index 2 [OK]

Hint: Middle index = floor(length/2), splice inserts at that index [OK]

Common Mistakes:

• Inserting at wrong index
• Replacing element instead of inserting
• Misunderstanding splice parameters

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

const nums = [1, 2, 3, 4, 5];
const mid = nums.length / 2;
nums.splice(mid, 0, 50);
console.log(nums);

medium

A. [1, 50, 2, 3, 4, 5]

B. [1, 2, 3, 4, 5, 50]

C. [1, 2, 3, 50, 4, 5]

D. [1, 2, 50, 3, 4, 5]

Solution

1. Step 1: Check mid calculation

   nums.length = 5, mid = 5 / 2 = 2.5 (a float).

2. Step 2: Understand splice behavior

   splice coerces 2.5 to integer 2 (ToInteger(2.5) = 2). Inserts 50 at index 2, shifting 3,4,5 right: [1, 2, 50, 3, 4, 5].

3. Final Answer:

   [1, 2, 50, 3, 4, 5] -> Option D

4. Quick Check:

   Float index coerced to 2 [OK]

Hint: Always floor length/2 for middle index [OK]

Common Mistakes:

• Confusing with unshift (insert at start)
• Confusing with push (append at end)
• Inserting at index 3 instead of 2

5. Given an array arr = [5, 10, 15, 20, 25], write a TypeScript function insertMiddle that inserts a given value exactly in the middle of the array. What will be the array after calling insertMiddle(arr, 12)?

hard

A. [5, 10, 12, 15, 20, 25]

B. [5, 10, 15, 12, 20, 25]

C. [12, 5, 10, 15, 20, 25]

D. [5, 10, 15, 20, 25, 12]

Solution

1. Step 1: Calculate middle index for odd length

   arr.length = 5, middle index = Math.floor(5/2) = 2.

2. Step 2: Insert 12 at index 2

   Using splice(2, 0, 12) inserts 12 before element at index 2 (which is 15), shifting elements right.

3. Final Answer:

   [5, 10, 12, 15, 20, 25] -> Option A

4. Quick Check:

   Inserted 12 at middle index 2 [OK]

Hint: Use Math.floor(length/2) for middle insertion [OK]

Common Mistakes:

• Inserting at wrong index for odd length
• Appending instead of inserting
• Replacing element instead of inserting