Array Deletion at End in DSA Typescript - Time & Space Complexity

Time Complexity: Array Deletion at End

O(1)

Understanding Time Complexity

We want to understand how fast it is to remove an item from the end of an array.

How does the time taken change as the array grows bigger?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

function deleteAtEnd(arr: number[]): number | undefined {
  return arr.pop();
}
    

This code removes the last element from the array and returns it.

Identify Repeating Operations

• Primary operation: Removing the last element using pop()
• How many times: Happens once per call, no loops or recursion inside

How Execution Grows With Input

Removing the last item takes the same small amount of work no matter how big the array is.

Input Size (n)	Approx. Operations
10	1
100	1
1000	1

Pattern observation: The work stays constant even as the array grows.

Final Time Complexity

Time Complexity: O(1)

This means removing the last element takes the same quick step no matter the array size.

Common Mistake

[X] Wrong: "Removing an element at the end takes longer as the array grows because it has to shift elements."

[OK] Correct: When deleting at the end, no elements need to move; only the last item is removed, so time stays the same.

Interview Connect

Knowing that removing from the end is fast helps you choose the right data structure and shows you understand array basics.

Self-Check

"What if we changed deletion to remove the first element instead? How would the time complexity change?"

Practice

1. What does the pop() method do when called on an array in TypeScript?

easy

A. Removes the last element from the array and returns it

B. Removes the first element from the array and returns it

C. Adds a new element to the end of the array

D. Returns the length of the array without changing it

Solution

1. Step 1: Understand the pop() method

   The pop() method removes the last element from an array and returns that element.

2. Step 2: Compare with other options

   Other options describe different methods: removing first element is shift(), adding element is push(), and returning length is length property.

3. Final Answer:

   Removes the last element from the array and returns it -> Option A

4. Quick Check:

   pop() removes last element = A [OK]

Hint: pop() always removes from the end of the array [OK]

Common Mistakes:

• Confusing pop() with shift()
• Thinking pop() adds elements
• Assuming pop() returns array length

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

easy

A. numbers.removeLast();

B. numbers.deleteEnd();

C. pop(numbers);

D. numbers.pop();

Solution

1. Step 1: Recall the correct method to remove last element

   The correct method is pop() called on the array object.

2. Step 2: Check syntax correctness

   Only numbers.pop(); is valid TypeScript syntax. Other options are not valid methods or functions.

3. Final Answer:

   numbers.pop(); -> Option D

4. Quick Check:

   Correct pop() syntax = B [OK]

Hint: Use arrayName.pop() to remove last element [OK]

Common Mistakes:

• Using non-existent methods like removeLast()
• Calling pop() as a standalone function
• Using incorrect method names

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

let fruits = ['apple', 'banana', 'cherry'];
let removed = fruits.pop();
console.log(fruits);
console.log(removed);

medium

A. ['apple', 'banana', 'cherry'] and 'cherry'

B. ['apple', 'banana', 'cherry'] and undefined

C. ['apple', 'banana'] and 'cherry'

D. ['apple', 'banana'] and 'banana'

Solution

1. Step 1: Understand pop() effect on array

   Calling pop() removes the last element 'cherry' from fruits and returns it.

2. Step 2: Trace the console.log outputs

   After pop, fruits is ['apple', 'banana'] and removed is 'cherry'.

3. Final Answer:

   ['apple', 'banana'] and 'cherry' -> Option C

4. Quick Check:

   pop() removes last element = D [OK]

Hint: pop() returns removed last element and shortens array [OK]

Common Mistakes:

• Expecting pop() to remove first element
• Thinking pop() returns the new array
• Confusing removed element with array length

4. Identify the error in the following TypeScript code that tries to remove the last element from an array items:

let items = [10, 20, 30];
items.pop;
console.log(items);

medium

A. Missing parentheses after pop method call

B. pop method does not exist on arrays

C. pop should be called as a standalone function

D. pop removes the first element, not last

Solution

1. Step 1: Check method call syntax

   The code uses items.pop; without parentheses, so the method is not called.

2. Step 2: Understand consequences

   Without parentheses, pop is just a reference, so the array remains unchanged.

3. Final Answer:

   Missing parentheses after pop method call -> Option A

4. Quick Check:

   pop() needs () to execute = A [OK]

Hint: Always use () to call methods like pop() [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking pop is a standalone function
• Confusing pop with shift

5. Given the array let nums = [5, 10, 15, 20];, which code snippet correctly removes the last two elements and returns the modified array?

hard

A. nums.pop(2); return nums;

B. nums.pop(); nums.pop(); return nums;

C. nums.splice(-2, 1); return nums;

D. nums.removeLast(2); return nums;

Solution

1. Step 1: Understand pop() removes one element at a time

   Calling pop() twice removes last two elements one by one.

2. Step 2: Check other options

   splice(-2, 1) removes only one element. pop(2) and removeLast(2) are invalid methods.

3. Final Answer:

   nums.pop(); nums.pop(); return nums; -> Option B

4. Quick Check:

   pop() removes one element; call twice for two [OK]

Hint: Call pop() twice to remove two elements from end [OK]

Common Mistakes:

• Trying pop() with arguments
• Using splice with incorrect parameters
• Using non-existent methods like removeLast