Array Insertion at End in DSA Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Insertion at End' mean?

It means adding a new element to the last position of an array, making the array one element longer.

beginner

In Rust, which method is commonly used to add an element at the end of a vector?

The push() method adds an element to the end of a vector in Rust.

intermediate

Why can't we directly insert at the end of a fixed-size array in Rust?

Fixed-size arrays have a set length that cannot change, so you cannot add elements beyond their size. Instead, use a vector for dynamic insertion.

intermediate

What happens if you try to insert an element beyond the current length of a vector without using push()?

You will get a runtime error or panic because vectors only allow adding elements at the end using push() or resizing methods.

beginner

Show a simple Rust code snippet to insert the number 10 at the end of a vector named numbers.

<pre>let mut numbers = vec![1, 2, 3];
numbers.push(10);</pre>

Which Rust method adds an element to the end of a vector?

A push()

B insert()

C append()

D extend()

The push() method adds a single element to the end of a vector.

Can you add an element to a fixed-size Rust array beyond its length?

A Yes, using push()

B No, fixed-size arrays cannot grow

C Yes, using insert()

D Yes, by resizing automatically

Fixed-size arrays have a fixed length and cannot grow. Use vectors for dynamic sizes.

What will happen if you try to access an index beyond the current vector length without pushing?

A It will add a new element automatically

B It will return None

C It will overwrite the last element

D It will panic at runtime

Accessing out-of-bound indices causes a runtime panic in Rust.

Which data structure should you use in Rust for dynamic insertion at the end?

A Vector

B Tuple

C Slice

D Fixed-size array

Vectors allow dynamic resizing and insertion at the end.

What is the output after this Rust code?

let mut v = vec![5, 6]; v.push(7);

A [5, 6]

B [7]

C [5, 6, 7]

D [6, 7]

The push adds 7 at the end, so the vector becomes [5, 6, 7].

Explain how to insert an element at the end of a collection in Rust and why vectors are preferred over fixed-size arrays for this.

Think about which Rust collection can change size.

Describe what happens internally when you use the push() method on a Rust vector.

Consider vector size and memory.

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