Array Insertion at End in DSA Python - Execution Trace

Concept Flow - Array Insertion at End

Start with array

↓

Check if array has space?

No→Resize array (if dynamic)

Yes↓

Insert new element at last index

↓

Update array size

↓

Done

This flow shows how we add a new element at the end of an array by checking space, inserting, and updating size.

Execution Sample

DSA Python

arr = [10, 20, 30]
size = 3
new_element = 40
arr.append(new_element)
size += 1
print(arr)

This code adds 40 at the end of the array and updates the size.

Execution Table

Step	Operation	Array Before	Action	Array After	Size Before	Size After
1	Start	[10, 20, 30]	Check space (dynamic array assumed)	[10, 20, 30]	3	3
2	Insert element 40 at end	[10, 20, 30]	Append 40	[10, 20, 30, 40]	3	4
3	Update size	[10, 20, 30, 40]	size = size + 1	[10, 20, 30, 40]	4	4
4	Print array	[10, 20, 30, 40]	Output array	[10, 20, 30, 40]	4	4

💡 Insertion done, size updated, array now has 4 elements.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
arr	[10, 20, 30]	[10, 20, 30]	[10, 20, 30, 40]	[10, 20, 30, 40]	[10, 20, 30, 40]
size	3	3	4	4	4
new_element	40	40	40	40	40

Key Moments - 3 Insights

Why do we update the size after insertion and not before?

Because the size variable represents the number of elements currently in the array. We only increase it after successfully adding the new element, as shown in step 3 of the execution_table.

What happens if the array is full and we try to insert?

In dynamic arrays (like Python lists), the array resizes automatically before insertion (step 1). In fixed-size arrays, insertion would fail or require manual resizing.

Why do we append the element at the end and not at the start?

Appending at the end keeps existing elements in order and is efficient. Inserting at the start would require shifting all elements, which is slower.

Visual Quiz - 3 Questions

Look at the execution_table, what is the size of the array after step 2?

A 3

B 2

C 4

D 0

💡 Hint

Check the 'Size After' column for step 2 in the execution_table.

At which step does the array actually get the new element 40?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' and 'Array After' columns in the execution_table.

If we forget to update the size after insertion, what will be the size shown after step 4?

A 5

B 3

C 4

D 0

💡 Hint

Refer to the 'size' variable changes in variable_tracker and the importance of step 3.

Concept Snapshot

Array Insertion at End:
- Add new element at last index
- Check space (resize if needed)
- Append element
- Update size variable
- Efficient for dynamic arrays

Full Transcript

This visual trace shows how to insert an element at the end of an array. We start with an array and its size. We check if there is space to add a new element. In dynamic arrays like Python lists, space is managed automatically. We then append the new element at the end and update the size variable to reflect the new number of elements. The final array shows the new element added at the end, and the size is increased by one.