Array Insertion at Middle Index in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert the value 99 at the middle index of the array.

DSA Javascript

const arr = [1, 2, 3, 4];
const mid = Math.floor(arr.length / 2);
arr.[1](mid, 0, 99);
console.log(arr);

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

Asplice

Bpush

Cslice

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using push or pop which add or remove elements only at the end.

Using slice which does not modify the original array.

The splice method inserts elements at a specified index without removing any elements when the delete count is 0.

2fill in blank

medium

Complete the code to find the middle index of the array correctly for insertion.

DSA Javascript

const arr = [10, 20, 30, 40, 50];
const mid = Math.[1](arr.length / 2);
arr.splice(mid, 0, 25);
console.log(arr);

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

Aceil

Bround

Cfloor

Dtrunc

Attempts:

3 left

💡 Hint

Common Mistakes

Using Math.ceil which rounds up and may cause index out of expected middle.

Using Math.round which rounds to nearest integer and may not be consistent.

Math.floor returns the largest integer less than or equal to the given number, which correctly finds the middle index for insertion.

3fill in blank

hard

Fix the error in the code to insert 100 at the middle index of the array.

DSA Javascript

let numbers = [5, 15, 25, 35];
let middle = Math.floor(numbers.length / 2);
numbers.[1](middle, 0, 100);
console.log(numbers);

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

Asplice

Bslice

Csplicee

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Misspelling splice as splicee.

Using slice which does not insert elements.

The correct method name is splice, not splicee or insert. Slice does not modify the array.

4fill in blank

hard

Fill both blanks to insert 77 at the middle index of the array without removing any elements.

DSA Javascript

const data = [2, 4, 6, 8, 10];
const midIndex = Math.[1](data.length / 2);
data.[2](midIndex, 0, 77);
console.log(data);

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

Afloor

Bceil

Csplice

Dslice

Attempts:

3 left

💡 Hint

Common Mistakes

Using Math.ceil which may select the wrong middle index.

Using slice instead of splice which does not modify the array.

Math.floor finds the correct middle index and splice inserts the element without removing any.

5fill in blank

hard

Fill all three blanks to insert the value 55 at the middle index of the array correctly.

DSA Javascript

let arr = [11, 22, 33, 44];
const middle = Math.[1](arr.length / 2);
arr.[2](middle, [3], 55);
console.log(arr);

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

Afloor

B0

Csplice

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete count 1 which removes an element.

Using Math.ceil which may select wrong index.

Math.floor finds the middle index, splice inserts without removing elements when delete count is 0.

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 first element with the new element

Solution

1. Step 1: Understand array indexing

   Arrays have positions starting from 0 to length-1. The middle index is roughly length/2.

2. Step 2: Define insertion at middle

   Inserting at middle means placing the new element at the middle index, shifting others 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 is array length divided by 2 [OK]

Common Mistakes:

• Confusing middle with start or end
• Replacing element instead of inserting
• Not shifting elements after insertion

2. Which of the following is the correct syntax to insert an element 'x' at the middle index of array 'arr' in JavaScript?

easy

A. arr.insert(Math.floor(arr.length / 2), x);

B. arr.add(Math.floor(arr.length / 2), x);

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

D. arr.push(Math.floor(arr.length / 2), x);

Solution

1. Step 1: Identify JavaScript method for insertion

   JavaScript arrays use splice(start, deleteCount, items...) to insert elements.

2. Step 2: Calculate middle index and insert

   Using Math.floor(arr.length / 2) gives middle index; splice with 0 deletes nothing and inserts 'x'.

3. Final Answer:

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

4. Quick Check:

   splice + middle index + 0 delete = insert [OK]

Hint: Use splice with 0 delete count to insert [OK]

Common Mistakes:

• Using non-existent insert or add methods
• Using push which adds only at end
• Not calculating middle index correctly

3. What will be the output of the following code?

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

medium

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

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

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

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

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

   Using splice(2, 0, 25) inserts 25 at index 2, shifting elements right.

3. Final Answer:

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

4. Quick Check:

   Insert at index 2 shifts right [OK]

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

Common Mistakes:

• Inserting at wrong index
• Appending instead of inserting
• Misunderstanding splice parameters

4. Identify the error in the following code that tries to insert 15 at the middle of array 'nums':

const nums = [5, 10, 20, 25];
nums.insert(nums.length / 2, 15);
console.log(nums);

medium

A. The middle index calculation is incorrect

B. 'insert' is not a valid array method in JavaScript

C. The element 15 should be added using push()

D. The array should be declared with let instead of const

Solution

1. Step 1: Check array method used

   JavaScript arrays do not have an 'insert' method; splice should be used instead.

2. Step 2: Confirm middle index calculation

   nums.length / 2 = 2 is correct, but method is invalid causing error.

3. Final Answer:

   'insert' is not a valid array method in JavaScript -> Option B

4. Quick Check:

   Use splice, not insert [OK]

Hint: Remember: JavaScript arrays use splice, not insert [OK]

Common Mistakes:

• Using non-existent insert method
• Ignoring method errors
• Confusing push with insert

5. Given an array arr = [1, 3, 5, 7, 9], write code to insert the number 4 exactly in the middle so that the array remains sorted. What will be the final array?

hard

A. [1, 3, 5, 7, 9, 4]

B. [1, 3, 5, 4, 7, 9]

C. [4, 1, 3, 5, 7, 9]

D. [1, 3, 4, 5, 7, 9]

Solution

1. Step 1: Find middle index for insertion

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

2. Step 2: Insert 4 at index 2 using splice

   arr.splice(2, 0, 4) inserts 4 before element 5, keeping array sorted.

3. Final Answer:

   [1, 3, 4, 5, 7, 9] -> Option D

4. Quick Check:

   Insert 4 at index 2 keeps order [OK]

Hint: Insert at floor(length/2) to keep sorted order [OK]

Common Mistakes:

• Inserting at wrong index breaking order
• Appending instead of inserting
• Not using splice correctly