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

Recall & Review

beginner

What does the push operation do in a stack?

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

beginner

In Rust, which data structure is commonly used to implement a stack for push operations?

A Vec<T> (vector) is commonly used because it allows efficient push and pop operations at the end.

intermediate

What happens if you push an element onto a full stack in a fixed-size stack implementation?

It causes a stack overflow error because there is no more space to add new elements.

intermediate

Explain the time complexity of the push operation on a stack implemented with a vector in Rust.

The push operation is usually O(1) (constant time) because it adds the element at the end of the vector, which is efficient.

beginner

Show the Rust code snippet to push an element 10 onto a stack represented by a vector named stack.

stack.push(10);

This adds the value 10 to the top of the stack.

What does the push operation do in a stack?

A Adds an element to the top

B Removes the top element

C Checks if the stack is empty

D Returns the bottom element

Push adds a new element to the top of the stack.

Which Rust data structure is best for implementing a stack with push operation?

A HashMap<K, V>

B LinkedList<T>

C Vec<T>

D BTreeSet<T>

Vec allows efficient push and pop at the end, ideal for stack.

What is the time complexity of push on a Rust vector stack?

A O(n)

B O(1)

C O(log n)

D O(n^2)

Push on a vector is usually O(1) as it adds at the end.

What error occurs if you push onto a full fixed-size stack?

A Stack overflow

B Stack underflow

C Null pointer exception

D Index out of bounds

Pushing on a full stack causes stack overflow.

How do you push the number 5 onto a Rust vector named stack?

A stack.append(5);

B stack.add(5);

C stack.insert(5);

D stack.push(5);

The push method adds an element to the end of the vector.

Describe how the push operation works on a stack and its effect on the stack's size.

Think about adding a new plate on top of a stack of plates.

Write a simple Rust code snippet to push an integer onto a stack implemented as a vector.

Use <code>stack.push(value);</code> where stack is a Vec.

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