Array Deletion at End in DSA Rust - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting the last element from the array?

Consider the Rust code below that deletes the last element from a vector. What will be printed?

DSA Rust

fn main() {
    let mut arr = vec![10, 20, 30, 40, 50];
    arr.pop();
    println!("{:?}", arr);
}

A [20, 30, 40, 50]

B [10, 20, 30, 40, 50]

C [10, 20, 30, 40]

D []

💡 Hint

The pop() method removes the last element from the vector.

The pop() method removes the last element (50) from the vector, so the remaining elements are [10, 20, 30, 40].

❓ Predict Output

intermediate

What happens if pop() is called on an empty vector?

What will be the output of the following Rust code?

DSA Rust

fn main() {
    let mut arr: Vec<i32> = Vec::new();
    let result = arr.pop();
    println!("{:?}", result);
}

A None

B Some(0)

C panic! at runtime

D Some(-1)

💡 Hint

pop() returns an Option type indicating if an element was removed.

Since the vector is empty, pop() returns None indicating no element was removed.

🔧 Debug

advanced

Why does this code cause a compile error when deleting the last element?

Identify the error in the Rust code below that tries to delete the last element from an array and fix it.

DSA Rust

fn main() {
    let arr = [1, 2, 3, 4];
    arr.pop();
    println!("{:?}", arr);
}

A Arrays have fixed size; pop() is not defined for arrays.

B pop() requires mutable reference but arr is immutable.

C pop() returns a value that must be assigned.

D println! macro syntax is incorrect.

💡 Hint

pop() works only on vectors, not fixed-size arrays.

Arrays in Rust have fixed size and do not support pop(). Only vectors support pop() to remove the last element.

🚀 Application

advanced

How to delete the last element and get the updated length?

Given a vector in Rust, which code snippet correctly deletes the last element and prints the updated length?

A arr.remove(arr.len()); println!("{}", arr.len());

B arr.pop(); println!("{}", arr.len());

C arr.pop(); println!("{}", arr.capacity());

D arr.pop(); println!("{}", arr.last());

💡 Hint

pop() removes last element; len() returns current length.

pop() removes the last element; len() returns the updated number of elements. remove(arr.len()) causes panic because index is out of bounds.

🧠 Conceptual

expert

What is the time complexity of deleting the last element from a Rust vector?

Consider a Rust vector with n elements. What is the time complexity of deleting the last element using pop()?

A O(n^2) - Quadratic time

B O(n) - Linear time

C O(log n) - Logarithmic time

D O(1) - Constant time

💡 Hint

pop() removes the last element without shifting others.

pop() removes the last element in constant time because no elements need to be shifted.

Practice

1. What happens when you remove the last element from a Rust Vec using pop()?

easy

A. The last element is removed and returned as Some(value).

B. The first element is removed and returned.

C. The entire vector is cleared.

D. The vector becomes immutable.

Solution

1. Step 1: Understand pop() behavior

   The pop() method removes the last element from the vector and returns it wrapped in Some(value) if the vector is not empty.

2. Step 2: Confirm it does not affect other elements

   Only the last element is removed; the rest of the vector remains unchanged.

3. Final Answer:

   The last element is removed and returned as Some(value). -> Option A

4. Quick Check:

   pop() removes last element [OK]

Hint: pop() removes and returns last element wrapped in Some [OK]

Common Mistakes:

• Thinking pop() removes the first element
• Assuming pop() clears the entire vector
• Believing pop() makes vector immutable

2. Which of the following is the correct syntax to remove the last element from a mutable vector v in Rust?

easy

A. v.erase_last();

B. v.remove_last();

C. v.delete_end();

D. v.pop();

Solution

1. Step 1: Recall Rust vector methods

   The standard method to remove the last element from a vector is pop().

2. Step 2: Check method names

   Methods like remove_last(), delete_end(), and erase_last() do not exist in Rust's Vec API.

3. Final Answer:

   v.pop(); -> Option D

4. Quick Check:

   Correct method to remove last element is pop() [OK]

Hint: Use pop() to remove last element from vector [OK]

Common Mistakes:

• Using non-existent methods like remove_last()
• Confusing pop() with remove() which removes by index
• Trying to use erase_last() or delete_end() which are invalid

3. What is the output of the following Rust code?

let mut v = vec![10, 20, 30];
let x = v.pop();
println!("{:?}", v);
println!("{:?}", x);

medium

A. [10, 20]
None

B. [10, 20, 30]
None

C. [10, 20]
Some(30)

D. [20, 30]
Some(10)

Solution

1. Step 1: Understand pop() effect on vector

   The pop() removes the last element, which is 30, and returns Some(30).

2. Step 2: Check vector after pop

   After removal, the vector contains [10, 20].

3. Final Answer:

   [10, 20] Some(30) -> Option C

4. Quick Check:

   pop() removes last element 30, vector left with [10, 20] [OK]

Hint: pop() returns last element and shortens vector [OK]

Common Mistakes:

• Expecting pop() to remove first element
• Assuming pop() returns None when vector is not empty
• Confusing vector contents after pop

4. Identify the error in the following Rust code that tries to remove the last element from a vector:

let v = vec![1, 2, 3];
v.pop();

medium

A. pop() method does not exist for vectors.

B. Cannot call pop() on an immutable vector.

C. pop() removes the first element, not the last.

D. The vector must be empty before calling pop().

Solution

1. Step 1: Check vector mutability

   The vector v is declared immutable with let. To modify it, it must be mutable.

2. Step 2: Understand pop() requirements

   The pop() method requires a mutable vector to remove the last element.

3. Final Answer:

   Cannot call pop() on an immutable vector. -> Option B

4. Quick Check:

   pop() needs mutable vector [OK]

Hint: Make vector mutable with 'mut' before pop() [OK]

Common Mistakes:

• Trying to pop from immutable vector
• Thinking pop() removes first element
• Assuming pop() works on empty vector without error

5. Given a vector v with elements [5, 10, 15, 20], write Rust code to remove the last two elements and print the resulting vector. What will be printed?

hard

A. [5, 10]

B. [5, 10, 15]

C. [15, 20]

D. [5, 10, 15, 20]

Solution

1. Step 1: Remove last element twice using pop()

   Calling pop() twice removes 20 then 15, leaving [5, 10].

2. Step 2: Print the vector after removals

   Printing v now shows [5, 10].

3. Final Answer:

   [5, 10] -> Option A

4. Quick Check:

   Two pops remove last two elements [OK]

Hint: Call pop() twice to remove last two elements [OK]

Common Mistakes:

• Removing only one element instead of two
• Confusing pop() with remove(index)
• Expecting vector to be empty after two pops