Array Deletion at Middle Index in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Deletion at Middle Index' mean?

It means removing an element from the middle position of an array, then shifting the remaining elements to fill the gap.

beginner

How do you find the middle index of an array with an odd number of elements?

Use the formula: middle index = Math.floor(array.length / 2). For example, if length is 5, middle index is 2 (0-based).

beginner

What happens to the array elements after deleting the middle element?

All elements after the deleted element move one position to the left to fill the empty spot, reducing the array size by one.

beginner

TypeScript code snippet: How to delete the middle element from an array?

const middleIndex = Math.floor(arr.length / 2);
arr.splice(middleIndex, 1);

beginner

Why is shifting elements necessary after deleting from the middle of an array?

Because arrays have fixed order and continuous indexes, shifting keeps the order intact and removes gaps.

What is the middle index of an array with 7 elements?

A 2

B 4

C 3

D 5

Middle index = Math.floor(7 / 2) = 3.

Which method removes elements from an array in TypeScript?

A push()

B splice()

C pop()

D slice()

splice() removes elements at a specified index.

After deleting the middle element, what happens to the array length?

A Increases by one

B Remains the same

C Doubles

D Decreases by one

Deleting an element reduces the array length by one.

If an array is [10, 20, 30, 40, 50], what is the array after deleting the middle element?

A [10, 20, 40, 50]

B [10, 20, 30, 40]

C [20, 30, 40, 50]

D [10, 30, 40, 50]

Middle element 30 (index 2) is removed; elements shift left.

Why do we use Math.floor when finding the middle index?

A To round down the index

B To round up the index

C To get a random index

D To double the index

Math.floor rounds down to get a valid integer index.

Explain how to delete the middle element from an array and what happens to the array after deletion.

Think about how arrays keep elements in order.

Write a TypeScript code snippet to delete the middle element from an array and show the resulting array.

Use splice with the middle index.

Practice

1. What does deleting the middle element from an array mean?
Example: [1, 2, 3, 4, 5] Delete the middle element.

easy

A. Remove the element at index 2 (value 3) from the array

B. Remove the first element (value 1) from the array

C. Remove the last element (value 5) from the array

D. Remove all elements except the middle one

Solution

1. Step 1: Identify the middle index of the array

   The array has 5 elements, so middle index = floor(5/2) = 2.

2. Step 2: Remove the element at the middle index

   Removing element at index 2 removes the value 3 from the array.

3. Final Answer:

   Remove the element at index 2 (value 3) from the array -> Option A

4. Quick Check:

   Middle index = 2, remove element 3 [OK]

Hint: Middle index = floor(length/2), remove that element [OK]

Common Mistakes:

• Removing first or last element instead of middle
• Using length/2 without floor for odd length
• Confusing index with value

2. Which TypeScript code correctly deletes the middle element from array arr?

easy

A. arr.removeAt(Math.floor(arr.length / 2));

B. arr.splice(Math.floor(arr.length / 2), 1);

C. arr.delete(Math.floor(arr.length / 2));

D. arr.pop(Math.floor(arr.length / 2));

Solution

1. Step 1: Identify correct method to remove element by index in TypeScript

   TypeScript arrays use splice(index, count) to remove elements at a specific index.

2. Step 2: Use Math.floor(arr.length / 2) to get middle index

   This expression correctly calculates the middle index for deletion.

3. Final Answer:

   arr.splice(Math.floor(arr.length / 2), 1); -> Option B

4. Quick Check:

   splice + floor middle index = correct deletion [OK]

Hint: Use splice with floor(length/2) to delete middle [OK]

Common Mistakes:

• Using non-existent methods like delete or removeAt
• Using pop() which removes last element only
• Not flooring the middle index calculation

3. What is the output of this TypeScript code?

let arr = [10, 20, 30, 40, 50];
arr.splice(Math.floor(arr.length / 2), 1);
console.log(arr);

medium

A. [20, 30, 40, 50]

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

C. [10, 20, 30, 50]

D. [10, 20, 40, 50]

Solution

1. Step 1: Calculate middle index

   Array length is 5, so middle index = floor(5/2) = 2.

2. Step 2: Remove element at index 2

   Element at index 2 is 30, so removing it results in [10, 20, 40, 50].

3. Final Answer:

   [10, 20, 40, 50] -> Option D

4. Quick Check:

   Removed element 30 at index 2 [OK]

Hint: Remove element at floor(length/2) index [OK]

Common Mistakes:

• Not flooring index, causing wrong removal
• Removing wrong element index
• Expecting original array unchanged

4. Find the error in this code that tries to delete the middle element:

let arr = [5, 10, 15, 20];
arr.splice(arr.length / 2, 1);
console.log(arr);

medium

A. console.log syntax is incorrect

B. splice method does not exist on arrays

C. Using arr.length / 2 without floor causes wrong index

D. splice removes all elements, not one

Solution

1. Step 1: Check middle index calculation

   arr.length / 2 = 4 / 2 = 2 (number), but for even length arrays, middle index should be floor(4/2) = 2, so this seems correct but in TypeScript splice expects integer index.

2. Step 2: Verify if index is integer

   arr.length / 2 is 2 (integer), so no error here. But if length was odd, it would be float. The main issue is that for even length arrays, middle is ambiguous; usually floor is used to pick index 2.

3. Step 3: Identify actual problem

   In this code, no floor is used but division results in integer 2, so no error. However, if length was odd, index would be float causing error. So best practice is to use Math.floor to ensure integer index.

4. Final Answer:

   Using arr.length / 2 without floor causes wrong index -> Option C

5. Quick Check:

   Always floor middle index for splice [OK]

Hint: Always floor middle index before splice [OK]

Common Mistakes:

• Not flooring index causing float error
• Thinking splice removes all elements
• Misunderstanding console.log usage

5. Given an array arr of even length, how can you delete the lower middle element?
Example: arr = [2, 4, 6, 8] After deletion, output should be [2, 6, 8].

hard

A. arr.splice(Math.floor(arr.length / 2) - 1, 1);

B. arr.splice(Math.ceil(arr.length / 2), 1);

C. arr.splice(arr.length / 2, 1);

D. arr.splice(arr.length / 2 + 1, 1);

Solution

1. Step 1: Understand middle elements in even length array

   For even length 4, middle indices are 1 and 2 (0-based). Lower middle is index 1.

2. Step 2: Calculate index to delete

   Math.floor(4/2) = 2, subtract 1 to get lower middle index = 1.

3. Step 3: Use splice to delete element at index 1

   arr.splice(1, 1) removes element 4, resulting in [2, 6, 8].

4. Final Answer:

   arr.splice(Math.floor(arr.length / 2) - 1, 1); -> Option A

5. Quick Check:

   Lower middle index = floor(length/2)-1 [OK]

Hint: Lower middle = floor(length/2) - 1 for even arrays [OK]

Common Mistakes:

• Deleting upper middle instead of lower middle
• Not adjusting index for zero-based arrays
• Using ceil instead of floor