Push Operation on Stack in DSA Rust - Execution Trace

Concept Flow - Push Operation on Stack

Create new element

↓

Check if stack is full?

Yes→Error: Stack Overflow

No↓

Place element on top

↓

Update top pointer

↓

Push complete

The push operation adds a new element on top of the stack if there is space, updating the top pointer.

Execution Sample

DSA Rust

stack = []
stack.push(10)
stack.push(20)
stack.push(30)

This code adds three elements (10, 20, 30) one by one to the stack.

Execution Table

Step	Operation	Nodes in Stack	Pointer Changes	Visual State
1	Initialize empty stack	[]	top = None	Stack: []
2	Push 10	[10]	top points to 10	Stack: 10 -> null
3	Push 20	[20, 10]	top points to 20	Stack: 20 -> 10 -> null
4	Push 30	[30, 20, 10]	top points to 30	Stack: 30 -> 20 -> 10 -> null
5	End	Stack full? No	top stable	Stack: 30 -> 20 -> 10 -> null

💡 No overflow, push operations complete successfully

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
stack	[]	[10]	[20, 10]	[30, 20, 10]	[30, 20, 10]
top	None	points to 10	points to 20	points to 30	points to 30

Key Moments - 3 Insights

Why does the top pointer change after each push?

Because the new element is placed on top, the top pointer must update to point to this new element as shown in steps 2, 3, and 4 in the execution_table.

What happens if the stack is full when pushing?

The push operation checks if the stack is full before adding. If full, it stops with an overflow error (not shown here because stack is not full). This is indicated in the concept_flow.

Why is the stack visual state shown with arrows?

The arrows represent the order of elements from top to bottom, showing how new elements are added on top, as seen in the visual state column of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what does the top pointer point to?

A 10

B 30

C 20

D None

💡 Hint

Check the 'Pointer Changes' column at step 3 in the execution_table.

At which step does the stack first contain three elements?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Nodes in Stack' column to see when three elements appear.

If we tried to push another element after step 4, what would happen according to concept_flow?

A Stack overflow error if stack is full

B The element is added without issue

C The top pointer moves to bottom

D The stack empties automatically

💡 Hint

Refer to the decision point in concept_flow checking if stack is full.

Concept Snapshot

Push Operation on Stack:
- Adds new element on top
- Checks for overflow before adding
- Updates top pointer to new element
- Stack grows from top down
- Visualized as top -> next -> ... -> null

Full Transcript

The push operation on a stack adds a new element on top if there is space. First, it creates the new element, then checks if the stack is full. If not full, it places the element on top and updates the top pointer to this new element. The stack grows by adding elements on top, and the top pointer always points to the newest element. This process repeats for each push. If the stack is full, the operation stops with an overflow error. The visual state shows the stack as a chain of elements from top to bottom.

Practice

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

easy

A. Removes the top element from the stack

B. Adds an element to the top of the stack

C. Returns the bottom element 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 B

4. Quick Check:

   Push = Add top element [OK]

Hint: Push always adds to the top of the stack [OK]

Common Mistakes:

• Confusing push with pop operation
• Thinking push removes elements
• Assuming push adds to the bottom

2. Which of the following is the correct Rust syntax to push an element 5 onto a stack implemented as a Vec<i32> named stack?

easy

A. stack.push(5);

B. stack.add(5);

C. stack.insert(5);

D. stack.append(5);

Solution

1. Step 1: Recall Rust Vec push method

   In Rust, Vec has a method push to add elements at the end (top of stack).

2. Step 2: Check method names

   add, insert, and append have different meanings or require different parameters.

3. Final Answer:

   stack.push(5); -> Option A

4. Quick Check:

   Vec push method = stack.push(5); [OK]

Hint: Use .push() to add elements to Vec stack [OK]

Common Mistakes:

• Using .add() which does not exist for Vec
• Confusing .insert() which needs index
• Using .append() which merges vectors

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

let mut stack = Vec::new();
stack.push(10);
stack.push(20);
stack.push(30);
println!("{:?}", stack);

medium

A. [10, 20, 30]

B. [30, 20, 10]

C. [10, 20]

D. Compilation error

Solution

1. Step 1: Trace push operations

   Elements 10, 20, and 30 are pushed in order, so stack contains [10, 20, 30].

2. Step 2: Understand Vec print format

   Printing with {:?} shows elements in insertion order, so output is [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option A

4. Quick Check:

   Push order preserved in Vec print [OK]

Hint: Vec prints elements in insertion order [OK]

Common Mistakes:

• Assuming stack prints top element first
• Confusing push order with pop order
• Expecting reversed output

4. Identify the error in this Rust code that tries to push an element onto a stack:

let stack = Vec::new();
stack.push(100);

medium

A. Missing semicolon after push

B. Vec::new() is incorrect syntax

C. push method does not exist for Vec

D. stack is immutable, cannot push

Solution

1. Step 1: Check variable mutability

   The variable stack is declared immutable by default, so push cannot modify it.

2. Step 2: Understand push method requirements

   push requires the vector to be mutable to add elements.

3. Final Answer:

   stack is immutable, cannot push -> Option D

4. Quick Check:

   Mutable vector needed for push [OK]

Hint: Declare stack as mutable with 'mut' to push [OK]

Common Mistakes:

• Forgetting to add 'mut' keyword
• Thinking Vec::new() is wrong syntax
• Assuming push is not a Vec method

5. You want to implement a stack using a Rust Vec<i32> and push elements 1, 2, 3 in that order. After pushing, you want to print the stack from top to bottom. Which code snippet correctly achieves this?

hard

A. let mut stack = Vec::new();
stack.push(1);
stack.push(2);
stack.push(3);
for i in stack.iter() {
println!("{}", i);
}

B. let mut stack = Vec::new();
stack.push(3);
stack.push(2);
stack.push(1);
for i in stack.iter() {
println!("{}", i);
}

C. let mut stack = Vec::new();
stack.push(1);
stack.push(2);
stack.push(3);
for i in stack.iter().rev() {
println!("{}", i);
}

D. let mut stack = Vec::new();
stack.push(1);
stack.push(2);
stack.push(3);
for i in stack.into_iter() {
println!("{}", i);
}

Solution

1. Step 1: Push elements in order

   Elements 1, 2, 3 are pushed in order, so stack is [1, 2, 3] with 3 at top.

2. Step 2: Print from top to bottom

   To print from top (last pushed) to bottom, iterate in reverse order using iter().rev().

3. Final Answer:

   Code snippet with stack.iter().rev() -> Option C

4. Quick Check:

   Reverse iteration prints top to bottom [OK]

Hint: Use .iter().rev() to print stack top to bottom [OK]

Common Mistakes:

• Printing in normal order shows bottom to top
• Pushing elements in reverse order
• Using into_iter() which consumes the stack