Array Insertion at Middle Index in DSA Rust - Build from Scratch

Array Insertion at Middle Index

📖 Scenario: You are managing a list of daily tasks. Sometimes, you need to add a new task right in the middle of your current list to keep things balanced.

🎯 Goal: Build a program that inserts a new task exactly in the middle of an existing list of tasks.

📋 What You'll Learn

Create a vector called tasks with these exact strings: "Clean", "Cook", "Shop", "Read"

Create a variable called new_task and set it to the string "Exercise"

Insert new_task into tasks at the middle index

Print the tasks vector after insertion

💡 Why This Matters

🌍 Real World

Managing and updating lists of tasks, events, or items is common in apps like to-do lists, calendars, and shopping lists.

💼 Career

Understanding how to insert elements into arrays or lists is a fundamental skill for software developers working with data structures.

1

Create the initial tasks list

Create a vector called tasks with these exact strings: "Clean", "Cook", "Shop", "Read"

DSA Rust

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

Hint

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

2

Add the new task variable

Create a variable called new_task and set it to the string "Exercise"

DSA Rust

fn main() {
    let mut tasks = vec!["Clean", "Cook", "Shop", "Read"];
    // Create new_task variable
    // Your code here
}

Hint

Use let to create a variable and assign the string "Exercise".

3

Insert the new task at the middle index

Insert new_task into tasks at the middle index. Calculate the middle index as tasks.len() / 2 and use tasks.insert().

DSA Rust

fn main() {
    let mut tasks = vec!["Clean", "Cook", "Shop", "Read"];
    let new_task = "Exercise";
    // Insert new_task at middle index
    // Your code here
}

Hint

Use tasks.len() / 2 to find the middle and tasks.insert(index, value) to insert.

4

Print the tasks after insertion

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

DSA Rust

fn main() {
    let mut tasks = vec!["Clean", "Cook", "Shop", "Read"];
    let new_task = "Exercise";
    let middle_index = tasks.len() / 2;
    tasks.insert(middle_index, new_task);
    // Print tasks vector
    // Your code here
}

Hint

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

Practice

1. What does inserting an element at the middle index of an array mean?

easy

A. Adding a new element at the end of the array

B. Replacing the middle element with a new one

C. Adding a new element exactly in the center, shifting others right

D. Removing the middle element from the array

Solution

1. Step 1: Understand middle index insertion

   Inserting at the middle means placing a new element at the center position, pushing existing elements to the right.

2. Step 2: Differentiate from other operations

   Replacing or removing elements changes existing data, but insertion adds a new element without deletion.

3. Final Answer:

   Adding a new element exactly in the center, shifting others right -> Option C

4. Quick Check:

   Middle insertion means add and shift [OK]

Hint: Middle insertion adds element, shifts others right [OK]

Common Mistakes:

• Thinking insertion replaces an element
• Confusing insertion with removal
• Assuming insertion always happens at end

2. Which Rust code correctly inserts the value 99 at the middle index of a vector named vec?

easy

A. vec.insert(vec.len() / 2, 99);

B. vec.push(99);

C. vec[vec.len() / 2] = 99;

D. vec.remove(vec.len() / 2); vec.push(99);

Solution

1. Step 1: Identify correct insertion method

   Rust's insert method adds an element at a given index, shifting others right.

2. Step 2: Calculate middle index and apply insert

   Using vec.len() / 2 gives the middle index; vec.insert places 99 there correctly.

3. Final Answer:

   vec.insert(vec.len() / 2, 99); -> Option A

4. Quick Check:

   Use insert with middle index [OK]

Hint: Use vec.insert(middle_index, value) to insert [OK]

Common Mistakes:

• Using push adds at end, not middle
• Assigning with vec[index] replaces, not inserts
• Removing then pushing changes order

3. What is the output of this Rust code?

let mut vec = vec![10, 20, 30, 40];
vec.insert(vec.len() / 2, 25);
println!("{:?}", vec);

medium

A. [10, 20, 30, 25, 40]

B. [10, 20, 25, 30, 40]

C. [10, 25, 20, 30, 40]

D. [25, 10, 20, 30, 40]

Solution

1. Step 1: Calculate middle index

   Vector length is 4, so middle index is 4 / 2 = 2.

2. Step 2: Insert 25 at index 2

   Inserting 25 at index 2 shifts elements at and after index 2 right: 30 and 40 move right.

3. Final Answer:

   [10, 20, 25, 30, 40] -> Option B

4. Quick Check:

   Insert at middle shifts elements right [OK]

Hint: Middle index = length/2; insert shifts right [OK]

Common Mistakes:

• Inserting at wrong index
• Confusing insert with replace
• Miscounting vector length

4. Identify the error in this Rust code that tries to insert 50 at the middle of vec:

let mut vec = vec![1, 2, 3, 4, 5];
let mid = vec.len() / 2;
vec[mid] = 50;
println!("{:?}", vec);

medium

A. Using assignment replaces element instead of inserting

B. vec.len() / 2 is incorrect middle index

C. vec is immutable, cannot modify

D. println! syntax is wrong

Solution

1. Step 1: Understand vec[mid] = 50;

   This replaces the element at index mid instead of inserting a new one.

2. Step 2: Correct method is insert

   To insert, use vec.insert(mid, 50); which shifts elements right.

3. Final Answer:

   Using assignment replaces element instead of inserting -> Option A

4. Quick Check:

   Assignment replaces, insert adds [OK]

Hint: Use insert() to add, not assignment [OK]

Common Mistakes:

• Replacing element instead of inserting
• Misunderstanding vector mutability
• Incorrect println! usage

5. Given a vector vec = vec![5, 10, 15, 20, 25, 30], write Rust code to insert 17 exactly in the middle so that the vector remains sorted. What will be the vector after insertion?

hard

A. [5, 10, 15, 20, 25, 30, 12]

B. [5, 10, 15, 12, 20, 25, 30]

C. [12, 5, 10, 15, 20, 25, 30]

D. [5, 10, 15, 17, 20, 25, 30]

Solution

1. Step 1: Find middle index for insertion

   Vector length is 6, middle index is 6 / 2 = 3.

2. Step 2: Insert 17 at index 3 to keep sorted order

   Inserting 17 at index 3 shifts elements 20, 25, 30 right, keeping order.

3. Final Answer:

   [5, 10, 15, 17, 20, 25, 30] -> Option D

4. Quick Check:

   Insert 17 at middle index 3 to keep sorted [OK]

Hint: Insert at length/2 to keep sorted vector [OK]

Common Mistakes:

• Inserting at wrong index breaking order
• Appending instead of inserting
• Replacing element instead of inserting