Push Operation on Stack in DSA Typescript - Build from Scratch

Push Operation on Stack

📖 Scenario: Imagine you have a stack of books. You want to add a new book on top of the stack. This is called a push operation in computer science.

🎯 Goal: You will create a stack using an array, set up a new book to add, perform the push operation to add the book on top, and then print the stack to see the new order.

📋 What You'll Learn

Create an array called stack with initial books: 'Book1', 'Book2', 'Book3'

Create a variable called newBook with the value 'Book4'

Use the push method on stack to add newBook

Print the stack array after the push operation

💡 Why This Matters

🌍 Real World

Stacks are used in many places like undo features in apps, browser history, and managing tasks in order.

💼 Career

Understanding stack operations like push is important for software development roles that involve data structure manipulation and algorithm design.

1

Create the initial stack

Create an array called stack with these exact books: 'Book1', 'Book2', 'Book3'

DSA Typescript

// Create the stack array with initial books
// Your code here

Hint

Use square brackets [] to create an array and separate items with commas.

2

Add the new book variable

Create a variable called newBook and set it to the string 'Book4'

DSA Typescript

const stack = ['Book1', 'Book2', 'Book3'];
// Create the newBook variable
// Your code here

Hint

Use const newBook = 'Book4'; to create the variable.

3

Push the new book onto the stack

Use the push method on stack to add newBook to the top of the stack

DSA Typescript

const stack = ['Book1', 'Book2', 'Book3'];
const newBook = 'Book4';
// Push newBook onto stack
// Your code here

Hint

Use stack.push(newBook); to add the new book on top.

4

Print the stack after push

Print the stack array to show the books after the push operation

DSA Typescript

const stack = ['Book1', 'Book2', 'Book3'];
const newBook = 'Book4';
stack.push(newBook);
// Print the stack array
// Your code here

Hint

Use console.log(stack); to print the array.

Practice

1. What does the push operation do in a stack data structure?

easy

A. Returns the bottom element of the stack

B. Removes the top element from the stack

C. Adds an element to the top of the stack

D. Checks if the stack is empty

Solution

1. Step 1: Understand stack behavior

   A stack follows Last In First Out (LIFO) principle, where elements are added or removed from the top.

2. Step 2: Define push operation

   The push operation adds a new element on top of the existing elements in the stack.

3. Final Answer:

   Adds an element to the top of the stack -> Option C

4. Quick Check:

   Push = Add top [OK]

Hint: Push always adds on top of stack [OK]

Common Mistakes:

• Confusing push with pop operation
• Thinking push removes elements
• Mixing stack with queue operations

2. Which of the following is the correct TypeScript syntax to push an element 5 into a stack array named stack?

easy

A. stack.push(5);

B. stack.add(5);

C. push(stack, 5);

D. stack.insert(5);

Solution

1. Step 1: Recall TypeScript array push method

   In TypeScript, arrays have a built-in method push() to add elements at the end (top for stack).

2. Step 2: Match syntax

   The correct syntax is calling push on the array with the element as argument: stack.push(5);

3. Final Answer:

   stack.push(5); -> Option A

4. Quick Check:

   Array push method = stack.push(value) [OK]

Hint: Use array.push(element) to push [OK]

Common Mistakes:

• Using non-existent methods like add or insert
• Calling push as a standalone function
• Forgetting parentheses after push

3. What will be the content of the stack after executing the following TypeScript code?

const stack: number[] = [];
stack.push(10);
stack.push(20);
stack.push(30);

medium

A. [30, 20, 10]

B. [10, 20, 30]

C. [10, 30, 20]

D. [20, 10, 30]

Solution

1. Step 1: Trace each push operation

   Initially, stack is empty []. After push(10), stack = [10]. After push(20), stack = [10, 20]. After push(30), stack = [10, 20, 30].

2. Step 2: Understand stack order

   The first pushed element is at index 0, last pushed at the end. So the array shows bottom to top as left to right.

3. Final Answer:

   [10, 20, 30] -> Option B

4. Quick Check:

   Push order = [10, 20, 30] [OK]

Hint: Stack array shows bottom to top left to right [OK]

Common Mistakes:

• Reversing the order of elements
• Confusing push with pop output
• Assuming push adds at start of array

4. Identify the error in the following TypeScript code that tries to push an element into a stack:

let stack: number[] = [1, 2, 3];
stack.push 4;

medium

A. Missing parentheses after push

B. Stack should be declared as const

C. push cannot be used on arrays

D. Missing semicolon after array declaration

Solution

1. Step 1: Check push method syntax

   The push method requires parentheses to pass the element: stack.push(4);. The code uses stack.push 4; which is invalid.

2. Step 2: Verify other parts

   Declaring stack with let is valid. push is valid on arrays. Semicolon is optional but not an error here.

3. Final Answer:

   Missing parentheses after push -> Option A

4. Quick Check:

   push() needs parentheses [OK]

Hint: Always use parentheses with push method [OK]

Common Mistakes:

• Omitting parentheses on method calls
• Thinking push is a property, not a method
• Confusing let and const errors

5. Given a stack implemented as an array, how can you push multiple elements [4, 5, 6] onto the stack in one operation while preserving their order (4 at bottom, 6 at top)?

hard

A. Use stack.unshift(...[4, 5, 6])

B. Use stack.push([4, 5, 6])

C. Use a loop to push each element from left to right

D. Use stack.push(...[4, 5, 6])

Solution

1. Step 1: Understand spread operator with push

   Using stack.push(...[4, 5, 6]) spreads the array elements as separate arguments, pushing 4, then 5, then 6 in order.

2. Step 2: Compare other options

   stack.push([4, 5, 6]) pushes the entire array as one element, not separate elements.
   Looping works but is multiple operations, not one.
   unshift adds elements at the start, not top of stack.

3. Final Answer:

   Use stack.push(...[4, 5, 6]) -> Option D

4. Quick Check:

   Spread operator with push adds multiple elements [OK]

Hint: Use spread operator ... with push for multiple elements [OK]

Common Mistakes:

• Pushing array as single element instead of separate
• Using unshift which adds at bottom
• Forgetting spread operator syntax