Array Insertion at Beginning in DSA Rust - Build from Scratch

Array Insertion at Beginning

📖 Scenario: You are managing a list of daily tasks. Sometimes, you get an urgent task that needs to be done first. You want to add this urgent task at the beginning of your task list.

🎯 Goal: Build a Rust program that starts with a list of tasks, then inserts a new urgent task at the beginning of the list, and finally shows the updated list.

📋 What You'll Learn

Create a vector called tasks with these exact strings: "email client", "write report", "team meeting"

Create a string variable called urgent_task with the exact value "fix server issue"

Insert the urgent_task at the beginning of the tasks vector

Print the tasks vector after insertion

💡 Why This Matters

🌍 Real World

Managing task lists or queues where urgent items need to be prioritized at the front.

💼 Career

Understanding how to manipulate arrays or lists is essential for software development, especially in scheduling, to-do apps, and real-time systems.

1

Create the initial task list

Create a vector called tasks with these exact strings: "email client", "write report", "team meeting"

DSA Rust

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

Hint

Use vec![...] to create a vector with the exact strings.

2

Add the urgent task variable

Create a string variable called urgent_task with the exact value "fix server issue"

DSA Rust

fn main() {
    let mut tasks = vec!["email client", "write report", "team meeting"];
    
    // Create the urgent_task string variable
    // Your code here
}

Hint

Use let urgent_task = "fix server issue"; to create the string variable.

3

Insert the urgent task at the beginning

Insert the urgent_task at the beginning of the tasks vector using the insert method

DSA Rust

fn main() {
    let mut tasks = vec!["email client", "write report", "team meeting"];
    let urgent_task = "fix server issue";
    
    // Insert urgent_task at index 0
    // Your code here
}

Hint

Use tasks.insert(0, urgent_task); to add the urgent task at the start.

4

Print the updated task list

Print the tasks vector using println! to show the updated list after insertion

DSA Rust

fn main() {
    let mut tasks = vec!["email client", "write report", "team meeting"];
    let urgent_task = "fix server issue";
    tasks.insert(0, urgent_task);
    
    // Print the tasks vector
    // Your code here
}

Hint

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

Practice

1. What happens when you insert an element at the beginning of a vector in Rust using insert(0, value)?

easy

A. The element is added at the end of the vector.

B. The element is added at the start, and all other elements shift right by one position.

C. The element replaces the first element without shifting others.

D. The vector size remains the same and no element is added.

Solution

1. Step 1: Understand insert(0, value) behavior

   In Rust, calling insert(0, value) on a vector adds the value at index 0.

2. Step 2: Effect on existing elements

   All existing elements shift one position to the right to make space for the new element.

3. Final Answer:

   The element is added at the start, and all other elements shift right by one position. -> Option B

4. Quick Check:

   Insert at index 0 shifts elements right [OK]

Hint: Insert at index 0 shifts all elements right [OK]

Common Mistakes:

• Thinking insert replaces the first element
• Assuming insert adds at the end
• Believing array size stays the same

2. Which of the following Rust code snippets correctly inserts the value 10 at the beginning of a vector named vec?

easy

A. vec.insert(0, 10);

B. vec.push(10);

C. vec[0] = 10;

D. vec.add(0, 10);

Solution

1. Step 1: Identify correct method for insertion at index

   Rust vectors use insert(index, value) to add elements at a specific position.

2. Step 2: Check each option

   vec.insert(0, 10); uses insert(0, 10), which inserts 10 at the start. vec.push(10); adds at the end. vec[0] = 10; replaces the first element without insertion. vec.add(0, 10); is invalid syntax.

3. Final Answer:

   vec.insert(0, 10); -> Option A

4. Quick Check:

   Use insert(0, value) to add at start [OK]

Hint: Use insert(0, value) to add at beginning [OK]

Common Mistakes:

• Using push() adds at end, not beginning
• Assigning vec[0] replaces element, no insertion
• Using non-existent method add()

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

let mut vec = vec![2, 3, 4];
vec.insert(0, 1);
println!("{:?}", vec);

medium

A. [2, 3, 4, 1]

B. [2, 3, 4]

C. [1, 3, 4]

D. [1, 2, 3, 4]

Solution

1. Step 1: Initial vector state

   The vector starts as [2, 3, 4].

2. Step 2: Insert 1 at index 0

   Using vec.insert(0, 1) adds 1 at the start, shifting others right.

3. Final Answer:

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

4. Quick Check:

   Insert at start shifts elements right [OK]

Hint: Insert at 0 adds element at front, shifts others right [OK]

Common Mistakes:

• Expecting element added at end
• Thinking insert replaces element
• Ignoring vector shift after insert

4. Identify the error in this Rust code:

let mut vec = vec![1, 2, 3];
vec.insert(5, 0);

medium

A. The index 5 is out of bounds for the vector of length 3.

B. The vector is immutable; it should be declared mutable.

C. The insert method parameters are reversed; index should be first, value second.

D. The insert method does not exist for vectors.

Solution

1. Step 1: Analyze the insert index

   The vector has length 3, valid insert indices are 0 to 3. Index 5 is out of bounds, causing runtime panic.

2. Step 2: Confirm syntax and mutability

   Parameters follow correct order insert(index, value); vector is declared mutable.

3. Final Answer:

   The index 5 is out of bounds for the vector of length 3. -> Option A

4. Quick Check:

   Insert index must be within vector bounds [OK]

Hint: Check insert(index, value) and index within vector length [OK]

Common Mistakes:

• Reversing insert parameters
• Using out-of-range index
• Forgetting to declare vector mutable

5. You have a vector vec = vec![10, 20, 30]. You want to insert multiple values [1, 2, 3] at the beginning efficiently. Which approach is best in Rust?

hard

A. Use a loop to insert each element at index 0 one by one.

B. Replace the original vector with the new elements only.

C. Create a new vector with the new elements, then extend it with the original vector.

D. Use vec.push() for each new element and then reverse the vector.

Solution

1. Step 1: Analyze inserting multiple elements at start

   Inserting one by one at index 0 shifts elements repeatedly, inefficient for multiple inserts.

2. Step 2: Efficient approach

   Create a new vector with new elements, then extend it with the original vector to combine efficiently.

3. Final Answer:

   Create a new vector with the new elements, then extend it with the original vector. -> Option C

4. Quick Check:

   Prepending by new vector + extend is efficient [OK]

Hint: Prepend multiple by new vector + extend original [OK]

Common Mistakes:

• Inserting elements one by one at index 0 (slow)
• Using push then reversing (extra steps)
• Replacing original vector loses data