Array Deletion at End in DSA Typescript

Mental Model

Removing the last item from a list means just cutting off the end so it no longer counts.

Analogy: Imagine a stack of books where you always take the top book off first. Deleting at the end is like removing the top book from the stack.

Index: 0   1   2   3   4
Array: [1]->[2]->[3]->[4]->[5]
Length: 5

Dry Run Walkthrough

Input: array: [1, 2, 3, 4, 5], delete last element

Goal: Remove the last element and reduce the array size by one

Step 1: Check if array is empty

[1]->[2]->[3]->[4]->[5], length=5

Why: We must ensure there is something to delete

Step 2: Reduce array length by one to remove last element

[1]->[2]->[3]->[4], length=4

Why: Cutting off the last element by shortening the array

Step 3: Return the updated array

[1]->[2]->[3]->[4], length=4

Why: Final array after deletion

Result:

Index: 0   1   2   3
Array: [1]->[2]->[3]->[4]
Length: 4

Annotated Code

DSA Typescript

class ArrayDeletion {
  private arr: number[];

  constructor(initialArray: number[]) {
    this.arr = initialArray;
  }

  deleteAtEnd(): number[] {
    if (this.arr.length === 0) {
      return this.arr; // nothing to delete
    }
    this.arr.length = this.arr.length - 1; // shorten array by one
    return this.arr;
  }
}

// Driver code
const arrayDeletion = new ArrayDeletion([1, 2, 3, 4, 5]);
console.log(arrayDeletion.deleteAtEnd().join(' -> ') + ' -> null');

if (this.arr.length === 0) {

Check if array is empty to avoid errors

this.arr.length = this.arr.length - 1;

Reduce array length by one to remove last element

return this.arr;

Return updated array after deletion

Output

1 -> 2 -> 3 -> 4 -> null

Complexity Analysis

Time: O(1) because deleting at the end just changes the length property without shifting elements

Space: O(1) because no extra space is needed, operation is in-place

vs Alternative: Compared to deleting at the start which requires shifting all elements O(n), deleting at the end is faster and simpler

Edge Cases

empty array

No deletion occurs, array remains empty

DSA Typescript

if (this.arr.length === 0) {

single element array

Deleting last element results in empty array

DSA Typescript

this.arr.length = this.arr.length - 1;

When to Use This Pattern

When you need to remove the last item quickly from a list, look for array deletion at end because it is the simplest and fastest removal.

Common Mistakes

Mistake: Trying to delete last element by shifting all elements left
Fix: Simply reduce the array length by one to remove last element without shifting

Mistake: Not checking if array is empty before deletion
Fix: Add a check for empty array to avoid errors

Summary

Deletes the last element of an array by reducing its length.

Use when you want to remove the last item quickly without rearranging other elements.

The key insight is that shortening the array length removes the last element instantly.

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