Array Insertion at Middle Index in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert the value 10 at the middle index of the vector.

DSA Rust

let mut numbers = vec![1, 2, 3, 4];
numbers.insert([1], 10);
println!("{:?}", numbers);

Drag options to blanks, or click blank then click option'

A1

B3

C0

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 1 or 3 instead of 2 causes insertion not exactly in the middle.

Using index 0 inserts at the start, not middle.

The middle index of a vector with 4 elements is 2. Inserting at index 2 places the new element in the middle.

2fill in blank

medium

Complete the code to insert the value 99 at the middle index of the vector.

DSA Rust

let mut values = vec![5, 6, 7, 8, 9];
values.insert([1], 99);
println!("{:?}", values);

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A2

B4

C3

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 inserts after the middle, not at the middle.

Using index 1 inserts before the middle.

For a vector with 5 elements, the middle index is 2 (integer division). Inserting at index 2 places the value in the middle.

3fill in blank

hard

Fix the error in the code to correctly insert 42 at the middle index.

DSA Rust

let mut data = vec![10, 20, 30, 40];
let mid = data.len() / [1];
data.insert(mid, 42);
println!("{:?}", data);

Drag options to blanks, or click blank then click option'

A3

B2

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as divisor returns full length, which appends to the end instead of inserting at the middle.

Using 3 or 4 gives wrong index.

To find the middle index, divide the length by 2. Using 2 correctly calculates the middle.

4fill in blank

hard

Fill both blanks to insert 100 at the middle index of the vector.

DSA Rust

let mut arr = vec![2, 4, 6, 8, 10, 12];
let middle = arr.len() [1] 2;
arr.insert(middle, [2]);
println!("{:?}", arr);

Drag options to blanks, or click blank then click option'

A/

B*

C100

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division for middle index.

Inserting wrong value.

Dividing length by 2 finds the middle index. Inserting 100 places the value at the middle.

5fill in blank

hard

Fill all three blanks to insert 77 at the middle index of the vector.

DSA Rust

let mut nums = vec![11, 22, 33, 44, 55];
let mid_index = nums.len() [1] 2;
nums.insert([2], [3]);
println!("{:?}", nums);

Drag options to blanks, or click blank then click option'

A/

Bmid_index

C77

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using a fixed index instead of middle index variable.

Inserting wrong value.

Divide length by 2 to get middle index, then insert 77 at that index.

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