Array Deletion at Beginning in DSA Python - Execution Trace

Concept Flow - Array Deletion at Beginning

Start with array

↓

Delete first element

↓

Shift all elements left by 1

↓

Reduce array size by 1

↓

End with updated array

This flow shows deleting the first element of an array by removing it and shifting all other elements left to fill the gap.

Execution Sample

DSA Python

arr = [10, 20, 30, 40]
# Delete first element
for i in range(1, len(arr)):
    arr[i-1] = arr[i]
arr.pop()
print(arr)

This code deletes the first element of the array by shifting elements left and removing the last duplicate.

Execution Table

Step	Operation	Array State	Pointer Changes	Visual State
0	Start	[10, 20, 30, 40]	i = None	10 -> 20 -> 30 -> 40 -> null
1	i=1: arr[0] = arr[1]	[20, 20, 30, 40]	i=1	20 -> 20 -> 30 -> 40 -> null
2	i=2: arr[1] = arr[2]	[20, 30, 30, 40]	i=2	20 -> 30 -> 30 -> 40 -> null
3	i=3: arr[2] = arr[3]	[20, 30, 40, 40]	i=3	20 -> 30 -> 40 -> 40 -> null
4	pop last element	[20, 30, 40]	i=None	20 -> 30 -> 40 -> null
5	End	[20, 30, 40]	i=None	20 -> 30 -> 40 -> null

💡 All elements shifted left, last duplicate removed, array size reduced by 1

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
arr	[10, 20, 30, 40]	[20, 20, 30, 40]	[20, 30, 30, 40]	[20, 30, 40, 40]	[20, 30, 40]	[20, 30, 40]
i	None	1	2	3	None	None

Key Moments - 3 Insights

Why do we shift elements left instead of just removing the first element?

Because arrays have fixed positions, removing the first element leaves a gap. Shifting left fills that gap, as shown in steps 1 to 3 in the execution_table.

Why do we pop the last element after shifting?

After shifting, the last element is duplicated. Popping removes this duplicate, reducing the array size, as shown in step 4.

What happens if the array is empty before deletion?

The loop does not run and pop would cause an error. We must check array size before deletion to avoid this, which is not shown here but important.

Visual Quiz - 3 Questions

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

A [20, 20, 30, 40]

B [20, 30, 30, 40]

C [20, 30, 40, 40]

D [10, 20, 30, 40]

💡 Hint

Check the 'Array State' column at step 2 in the execution_table.

At which step is the last element removed from the array?

A Step 4

B Step 5

C Step 3

D Step 1

💡 Hint

Look for the 'pop last element' operation in the execution_table.

If the initial array was [5, 15, 25], what would be the final array after deletion?

A [5, 15]

B [25]

C [15, 25]

D [5, 15, 25]

💡 Hint

Deletion removes first element and shifts left, check variable_tracker logic.

Concept Snapshot

Array Deletion at Beginning:
- Remove first element by shifting all elements left
- Last element becomes duplicate after shift
- Remove last element to reduce size
- Array size decreases by 1
- Must check array not empty before deletion

Full Transcript

This concept shows how to delete the first element of an array. We start with the full array. Then, we shift every element one position to the left to fill the gap left by the removed element. This causes the last element to be duplicated. To fix this, we remove the last element, reducing the array size by one. The final array no longer contains the original first element. This process is shown step-by-step in the execution table and variable tracker. Beginners often wonder why shifting is needed and why the last element is removed. Also, care must be taken if the array is empty before deletion.