Push Operation on Stack in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the push operation do in a stack?

It adds a new element to the top of the stack, increasing its size by one.

beginner

In a stack, which end do we add elements to during a push operation?

We add elements to the top of the stack.

intermediate

What happens if you try to push an element onto a full stack (stack overflow)?

The push operation fails because there is no space to add a new element.

beginner

Show the TypeScript code snippet to push an element onto a stack represented by an array.

stack.push(element); // Adds 'element' to the top of the stack array

beginner

Why is the push operation on a stack considered Last In, First Out (LIFO)?

Because the last element pushed onto the stack is the first one to be removed.

What does the push operation do in a stack?

A Adds an element to the top

B Removes an element from the bottom

C Removes an element from the top

D Adds an element to the bottom

Push adds an element to the top of the stack.

If a stack is full, what happens when you try to push a new element?

A The element is added anyway

B The stack resets

C The bottom element is removed

D The push operation fails (overflow)

Push fails because there is no space to add new elements.

Which data structure principle does push operation follow?

A First In, First Out (FIFO)

B Random Access

C Last In, First Out (LIFO)

D Priority Queue

Stack uses LIFO, so push adds to the top.

In TypeScript, how do you push an element '5' onto a stack array named 'stack'?

A stack.add(5);

B stack.push(5);

C stack.insert(5);

D stack.append(5);

The push method adds an element to the end (top) of the array.

After pushing elements 1, 2, then 3 onto an empty stack, what is the top element?

A 3

B 2

C 1

D Stack is empty

The last pushed element (3) is at the top.

Explain the push operation on a stack and how it affects the stack's order.

Think about where the new element goes and what happens if the stack is full.

Write a simple TypeScript function to push a number onto a stack represented by an array.

Use array.push(element) inside the function.

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