Array Deletion at End in DSA Rust - Build from Scratch

Array Deletion at End

📖 Scenario: You are managing a list of tasks to do today. Sometimes, you finish the last task and want to remove it from your list.

🎯 Goal: Build a Rust program that creates a list of tasks, sets up a counter for how many tasks to remove, removes that many tasks from the end of the list, and then shows the remaining tasks.

📋 What You'll Learn

Create a vector called tasks with these exact strings: "Wash dishes", "Do laundry", "Write report", "Call mom", "Read book"

Create a variable called remove_count and set it to 2

Use a for loop with variable _ to remove the last element from tasks exactly remove_count times

Print the tasks vector after removals

💡 Why This Matters

🌍 Real World

Managing lists of tasks or items where you often remove the last entries, like undo stacks or recent files.

💼 Career

Understanding how to manipulate arrays or lists is essential for software development, especially in managing dynamic data.

1

Create the tasks list

Create a vector called tasks with these exact strings: "Wash dishes", "Do laundry", "Write report", "Call mom", "Read book"

DSA Rust

# Create the tasks vector with the given strings
# Your code here

Hint

Use let mut tasks = vec![...] to create a mutable vector with the exact strings inside.

2

Set the number of tasks to remove

Create a variable called remove_count and set it to 2

DSA Rust

fn main() {
    let mut tasks = vec!["Wash dishes", "Do laundry", "Write report", "Call mom", "Read book"];
    
    // Create remove_count variable and set it to 2
    # Your code here
}

Hint

Use let remove_count = 2; to create the variable.

3

Remove tasks from the end

Use a for loop with variable _ to remove the last element from tasks exactly remove_count times using pop()

DSA Rust

fn main() {
    let mut tasks = vec!["Wash dishes", "Do laundry", "Write report", "Call mom", "Read book"];
    let remove_count = 2;
    
    // Remove last task remove_count times
    # Your code here
}

Hint

Use for _ in 0..remove_count and inside the loop call tasks.pop() to remove the last element.

4

Print the remaining tasks

Print the tasks vector after removals using println!("{:?}", tasks)

DSA Rust

fn main() {
    let mut tasks = vec!["Wash dishes", "Do laundry", "Write report", "Call mom", "Read book"];
    let remove_count = 2;
    for _ in 0..remove_count {
        tasks.pop();
    }
    
    // Print the tasks vector
    # Your code here
}

Hint

Use println!("{:?}", tasks); to print the vector in debug format.

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