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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after inserting elements at the end of a Rust vector?

Consider the following Rust code that inserts elements at the end of a vector. What will be printed?

DSA Rust

fn main() {
    let mut v = vec![1, 2, 3];
    v.push(4);
    v.push(5);
    println!("{:?}", v);
}

A [1, 2, 3, 4, 5]

B [4, 5, 1, 2, 3]

C [1, 2, 3]

D [5, 4, 3, 2, 1]

💡 Hint

Remember that push adds elements to the end of the vector.

The push method appends elements to the end of the vector, so after pushing 4 and 5, the vector becomes [1, 2, 3, 4, 5].

❓ Predict Output

intermediate

What happens if you push an element to an empty vector?

What will be the output of this Rust code?

DSA Rust

fn main() {
    let mut v: Vec<i32> = Vec::new();
    v.push(10);
    println!("{:?}", v);
}

A []

B [10]

C [0, 10]

D Compilation error

💡 Hint

An empty vector can have elements added with push.

The vector starts empty. After pushing 10, it contains one element: [10].

❓ Predict Output

advanced

What is the output after multiple insertions and a pop operation?

Analyze the following Rust code and determine the printed vector.

DSA Rust

fn main() {
    let mut v = vec![5, 6];
    v.push(7);
    v.push(8);
    v.pop();
    println!("{:?}", v);
}

A [8, 7, 6, 5]

B [5, 6, 7, 8]

C [5, 6, 7]

D [5, 6]

💡 Hint

pop removes the last element added.

After pushing 7 and 8, vector is [5, 6, 7, 8]. pop removes 8, so vector becomes [5, 6, 7].

🔧 Debug

advanced

Why does this Rust code fail to compile when inserting at the end?

Identify the error in this Rust code and what error message it produces.

DSA Rust

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

A error: mismatched types

B error: expected `;` after expression

C error: no method named `push` found for type `Vec<i32>`

D error: cannot borrow immutable variable `v` as mutable

💡 Hint

Check if the vector is mutable before pushing.

The vector `v` is declared immutable with `let`. The push method requires a mutable vector, so the compiler errors on borrowing immutable `v` as mutable.

🧠 Conceptual

expert

What is the time complexity of inserting an element at the end of a Rust vector?

Consider a Rust vector with n elements. What is the average time complexity of the push operation that inserts an element at the end?

A O(1) amortized time

B O(n) always

C O(log n)

D O(n^2)

💡 Hint

Think about how vectors resize internally.

Rust vectors allocate extra space. Most push operations are O(1), but occasionally resizing takes O(n). Averaged over many pushes, the time is O(1) amortized.

Practice

1. What does inserting an element at the end of an array mean in simple terms?

easy

A. Sorting the array in ascending order

B. Removing the first item from the array

C. Replacing the first item in the array

D. Adding a new item after the last existing item in the array

Solution

1. Step 1: Understand array structure

   An array is a list of items stored in order, starting from the first to the last.

2. Step 2: Define insertion at the end

   Inserting at the end means placing a new item right after the last item, extending the array by one.

3. Final Answer:

   Adding a new item after the last existing item in the array -> Option D

4. Quick Check:

   Insert at end = Add after last [OK]

Hint: Think: new item goes after the last one [OK]

Common Mistakes:

• Confusing insertion at end with removal
• Thinking insertion replaces an item
• Mixing insertion with sorting

2. Which Rust code snippet correctly inserts the value 10 at the end of a mutable vector named vec?

easy

A. vec.push(10);

B. vec.insert(0, 10);

C. vec[vec.len()] = 10;

D. vec.append(10);

Solution

1. Step 1: Identify correct method to add at end

   In Rust, push adds an element to the end of a vector.

2. Step 2: Check other options

   insert(0, 10) adds at start, vec[vec.len()] = 10 causes error (index out of bounds), append(10) is invalid syntax.

3. Final Answer:

   vec.push(10); -> Option A

4. Quick Check:

   Use push() to add at end [OK]

Hint: Use push() to add at the end of a vector [OK]

Common Mistakes:

• Using insert with wrong index
• Trying to assign to vec[vec.len()] directly
• Using append with a single value

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

let mut numbers = vec![1, 2, 3];
numbers.push(4);
println!("{:?}", numbers);

medium

A. [1, 2, 3]

B. [4, 1, 2, 3]

C. [1, 2, 3, 4]

D. Compilation error

Solution

1. Step 1: Understand initial vector

   The vector numbers starts as [1, 2, 3].

2. Step 2: Apply push operation

   numbers.push(4) adds 4 at the end, making it [1, 2, 3, 4].

3. Final Answer:

   [1, 2, 3, 4] -> Option C

4. Quick Check:

   push(4) adds 4 at end [OK]

Hint: push() adds element at the end [OK]

Common Mistakes:

• Thinking push adds at start
• Expecting original vector unchanged
• Confusing output format

4. Identify the error in this Rust code that tries to insert 5 at the end of a vector:

let numbers = vec![1, 2, 3];
numbers.push(5);

medium

A. Cannot push because vector is immutable

B. push method does not exist for vectors

C. Syntax error in push call

D. No error, code runs fine

Solution

1. Step 1: Check vector mutability

   The vector numbers is declared without mut, so it is immutable.

2. Step 2: Understand push requirements

   push requires the vector to be mutable to add elements.

3. Final Answer:

   Cannot push because vector is immutable -> Option A

4. Quick Check:

   push needs mutable vector [OK]

Hint: Declare vector as mutable to push [OK]

Common Mistakes:

• Forgetting to add mut keyword
• Assuming push works on immutable vectors
• Misreading error as syntax problem

5. Given a vector vec with elements [2, 4, 6], write Rust code to insert the number 8 at the end and then remove the first element. What will be the final vector?

hard

A. [2, 4, 6, 8]

B. [4, 6, 8]

C. [8, 2, 4, 6]

D. [2, 4, 8]

Solution

1. Step 1: Insert 8 at the end

   Using vec.push(8), vector becomes [2, 4, 6, 8].

2. Step 2: Remove the first element

   Using vec.remove(0), removes 2, vector becomes [4, 6, 8].

3. Final Answer:

   [4, 6, 8] -> Option B

4. Quick Check:

   push then remove first = [4,6,8] [OK]

Hint: Push adds end, remove(0) deletes first [OK]

Common Mistakes:

• Removing last instead of first element
• Not updating vector after push
• Confusing remove index