Array Deletion at Beginning in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting the first element?

Consider the following TypeScript code that deletes the first element from an array. What will be the printed output?

DSA Typescript

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

A [10, 20, 30, 40]

B [20, 30, 40]

C [30, 40]

D []

💡 Hint

The shift() method removes the first element of the array.

The shift() method removes the first element (10) from the array. The remaining elements are [20, 30, 40].

❓ Predict Output

intermediate

What happens if we delete the first element from an empty array?

What will be the output of the following TypeScript code?

DSA Typescript

const arr: number[] = [];
const removed = arr.shift();
console.log(removed);
console.log(arr);

A

0
[]

B

null
[]

C

undefined
[]

D

Error
[]

💡 Hint

shift() returns undefined if the array is empty.

Calling shift() on an empty array returns undefined. The array remains empty.

🔧 Debug

advanced

Why does this code not delete the first element?

Look at this TypeScript code. It tries to delete the first element but fails. What is the reason?

DSA Typescript

const arr = [1, 2, 3, 4];
arr.pop();
console.log(arr);

A pop() removes all elements

B pop() does not modify the array

C pop() throws an error on non-empty arrays

D pop() removes the last element, not the first

💡 Hint

Check what pop() does compared to shift().

The pop() method removes the last element of the array, not the first. To remove the first element, use shift().

🧠 Conceptual

advanced

What is the time complexity of deleting the first element in a TypeScript array?

When you delete the first element of an array using shift(), what is the time complexity and why?

A O(n), because all elements must be shifted left

B O(log n), because of internal binary search

C O(1), because shift() removes the first element instantly

D O(n^2), because each element is copied twice

💡 Hint

Think about what happens to the rest of the elements after removing the first.

Deleting the first element requires shifting all other elements one position left, so it takes O(n) time.

🚀 Application

expert

Efficiently delete the first element multiple times

You want to delete the first element from a large array many times efficiently. Which approach is best?

A Use a queue data structure instead of an array

B Use shift() repeatedly on the array

C Use pop() repeatedly on the array

D Create a new array each time without the first element

💡 Hint

Think about data structures optimized for removing from the front.

Queues are designed for efficient removal from the front (O(1)), unlike arrays where shift() is O(n).

Practice

1. What does deleting the first element of an array using array.shift() do to the array?

easy

A. Removes the last element of the array

B. Removes the first element and shifts all other elements left

C. Deletes the entire array

D. Adds a new element at the beginning

Solution

1. Step 1: Understand shift() method

   The shift() method removes the first element of the array.

2. Step 2: Effect on array elements

   After removal, all other elements move one position to the left to fill the gap.

3. Final Answer:

   Removes the first element and shifts all other elements left -> Option B

4. Quick Check:

   shift() removes first element [OK]

Hint: Remember: shift() removes from start, pop() removes from end [OK]

Common Mistakes:

• Confusing shift() with pop()
• Thinking shift() deletes entire array
• Assuming shift() adds elements

2. Which of the following is the correct syntax to remove the first element from an array named nums in TypeScript?

easy

A. nums.shift()

B. nums.removeFirst()

C. nums.pop()

D. nums.delete(0)

Solution

1. Step 1: Identify the method to remove first element

   The correct method to remove the first element in TypeScript arrays is shift().

2. Step 2: Check other options

   pop() removes last element, removeFirst() and delete(0) are invalid methods.

3. Final Answer:

   nums.shift() -> Option A

4. Quick Check:

   Use shift() to remove first element [OK]

Hint: Use shift() to remove first element, pop() for last [OK]

Common Mistakes:

• Using pop() instead of shift()
• Using non-existent methods like removeFirst()
• Trying to delete with delete(0) which is invalid

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

let arr = [10, 20, 30, 40];
arr.shift();
console.log(arr);

medium

A. [40]

B. [10, 20, 30, 40]

C. [30, 40]

D. [20, 30, 40]

Solution

1. Step 1: Initial array and shift operation

   The array starts as [10, 20, 30, 40]. Calling shift() removes the first element 10.

2. Step 2: Resulting array after shift

   After removal, the array becomes [20, 30, 40].

3. Final Answer:

   [20, 30, 40] -> Option D

4. Quick Check:

   shift() removes first element, rest remain [OK]

Hint: shift() removes first element, so array starts from second element [OK]

Common Mistakes:

• Expecting original array unchanged
• Thinking shift() removes last element
• Confusing output with pop() effect

4. Consider this TypeScript code snippet:

let numbers = [5, 10, 15];
numbers.shift;
console.log(numbers);

What is the issue and how to fix it?

medium

A. Missing parentheses after shift; fix by using numbers.shift()

B. shift is not a valid method; use pop() instead

C. Array is empty; no fix needed

D. shift() removes last element; use unshift() instead

Solution

1. Step 1: Identify the method call mistake

   The code uses numbers.shift without parentheses, so the method is not called.

2. Step 2: Correct method call syntax

   Adding parentheses numbers.shift() calls the method and removes the first element.

3. Final Answer:

   Missing parentheses after shift; fix by using numbers.shift() -> Option A

4. Quick Check:

   Method calls need parentheses [OK]

Hint: Always add () to call methods like shift() [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Using pop() instead of shift() incorrectly
• Misunderstanding shift() removes first element

5. You have an array let fruits = ['apple', 'banana', 'cherry', 'date'];. You want to remove the first two fruits efficiently. Which code snippet correctly does this?

hard

A. fruits.shift(2);

B. fruits.pop(); fruits.pop();

C. fruits.splice(0, 2);

D. fruits.delete(0); fruits.delete(1);

Solution

1. Step 1: Understand removing multiple elements

   fruits.shift(2); fruits.shift(2); is incorrect: shift() takes no arguments (ignores 2) and removes only the first element.

2. Step 2: Using splice for efficient removal

   splice(0, 2) removes two elements starting at index 0 in one operation.

3. Step 3: Check other options

   pop() removes from end, delete() is invalid for arrays.

4. Final Answer:

   fruits.splice(0, 2); -> Option C

5. Quick Check:

   Use splice to remove multiple from start efficiently [OK]

Hint: Use splice(0, n) to remove n elements from start at once [OK]

Common Mistakes:

• Using shift(2) which only removes one element
• Using pop() which removes from end
• Using invalid delete() method