Array Traversal Patterns in DSA Python - Execution Trace

Concept Flow - Array Traversal Patterns

Start at index 0

↓

Check: index < length?

No→End traversal

Yes↓

Access element at index

↓

Process element

↓

Update index (e.g., index+1)

↩Back to Check

Start from the first element, check if index is within array bounds, access and process the element, then move to the next index until all elements are visited.

Execution Sample

DSA Python

arr = [10, 20, 30]
index = 0
while index < len(arr):
    print(arr[index])
    index += 1

Traverse the array from start to end, printing each element.

Execution Table

Step	Operation	Index	Condition (index < len(arr))	Element Accessed	Output	Next Index
1	Start traversal	0	0 < 3 = True	arr[0] = 10	10	1
2	Continue traversal	1	1 < 3 = True	arr[1] = 20	20	2
3	Continue traversal	2	2 < 3 = True	arr[2] = 30	30	3
4	Check condition	3	3 < 3 = False	None	None	End

💡 Traversal ends when index reaches array length (3), condition becomes false.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
index	0	1	2	3	3
Output	None	10	20	30	30

Key Moments - 3 Insights

Why does the loop stop when index equals the array length?

Because arrays are zero-indexed, valid indices are 0 to length-1. When index equals length, it is outside the array bounds, so the condition fails (see execution_table row 4).

What happens if we forget to update the index inside the loop?

The index stays the same, causing an infinite loop because the condition never becomes false. The execution_table shows index increasing each step to avoid this.

Why do we access arr[index] only after checking the condition?

To avoid accessing invalid memory or causing errors. The condition ensures index is valid before accessing the element (see execution_table columns 'Condition' and 'Element Accessed').

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'index' after Step 2?

A 2

B 1

C 3

D 0

💡 Hint

Check the 'Next Index' column in execution_table row 2.

At which step does the condition 'index < len(arr)' become false?

A Step 3

B Step 2

C Step 4

D Step 1

💡 Hint

Look at the 'Condition' column in execution_table row 4.

If the array had 5 elements instead of 3, how many steps would the traversal take?

A 5 steps

B 6 steps

C 4 steps

D 3 steps

💡 Hint

Traversal steps = number of elements + 1 for the final condition check (see execution_table rows).

Concept Snapshot

Array Traversal Patterns:
- Start at index 0
- Loop while index < array length
- Access and process element at current index
- Increment index to move forward
- Stop when index reaches array length

Full Transcript

Array traversal means visiting each element in order from start to end. We begin at index zero and check if the index is less than the array's length. If yes, we access the element at that index and do something with it, like printing. Then we increase the index by one and repeat. When the index equals the length, we stop because there are no more elements. This pattern ensures every element is visited exactly once safely.