Array Insertion at End in DSA Rust - Execution Trace

Concept Flow - Array Insertion at End

Start with array

↓

Check if space available?

No→Resize array

Yes↓

Insert new element at end

↓

Update array size

↓

Done

This flow shows how we insert an element at the end of an array by checking space, resizing if needed, inserting the element, and updating the size.

Execution Sample

DSA Rust

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

This code adds the number 4 at the end of the array [1, 2, 3] and prints the updated array.

Execution Table

Step	Operation	Array State Before	Pointer Changes	Array State After
1	Start with array	[1, 2, 3]	head -> index 0, size=3	[1, 2, 3]
2	Check space for new element	[1, 2, 3]	size=3, capacity=3	[1, 2, 3] (full)
3	Resize array (capacity grows)	[1, 2, 3]	capacity increased to 6	[1, 2, 3, _, _, _]
4	Insert element 4 at end	[1, 2, 3, _, _, _]	size=3 -> 4	[1, 2, 3, 4, _, _]
5	Update size	[1, 2, 3, 4, _, _]	size=4	[1, 2, 3, 4]
6	Print array	[1, 2, 3, 4]	size=4	[1, 2, 3, 4]

💡 Insertion complete, array size updated to 4

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
arr	[1, 2, 3]	[1, 2, 3]	[1, 2, 3, _, _, _]	[1, 2, 3, 4, _, _]	[1, 2, 3, 4]
size	3	3	3	4	4
capacity	3	3	6	6	6

Key Moments - 3 Insights

Why do we need to resize the array before inserting?

Because the array's capacity is full at step 2 (size equals capacity), we must increase capacity to hold the new element, as shown in step 3.

What happens to the array size after insertion?

At step 4 and 5, the size variable increases from 3 to 4 to reflect the new element added at the end.

Why does the array show underscores (_) after resizing?

The underscores represent empty slots reserved after resizing capacity, visible at step 3 before the new element is inserted.

Visual Quiz - 3 Questions

Look at the execution table, what is the capacity of the array after step 3?

A 6

B 3

C 4

D Undefined

💡 Hint

Check the 'Pointer Changes' column at step 3 in the execution table.

At which step does the array size increase?

A Step 2

B Step 4

C Step 3

D Step 6

💡 Hint

Look at the 'Pointer Changes' column for size changes in the execution table.

If the array had capacity 5 instead of 3 initially, which step would be skipped?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Step 3 is resizing the array when capacity is full, see execution table step 3.

Concept Snapshot

Array Insertion at End:
- Check if array has space (size < capacity)
- If full, resize array to bigger capacity
- Insert new element at index = size
- Increase size by 1
- Array elements remain in order
- Resizing copies old elements to new bigger array

Full Transcript

This visual trace shows how to insert an element at the end of an array. We start with an array of size 3 and capacity 3. Since the array is full, we resize it to capacity 6, adding empty slots. Then we insert the new element at the end, update the size to 4, and print the updated array. The variable tracker shows how size and capacity change. Key moments clarify why resizing is needed and how size updates. The quiz tests understanding of capacity, size changes, and skipping resizing if capacity is enough.

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