Why Two Pointer Technique Beats Brute Force in DSA Python - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the left pointer at the start of the list.

DSA Python

left = [1]

Drag options to blanks, or click blank then click option'

A0

B-1

C1

Dlen(arr)

Attempts:

3 left

💡 Hint

Common Mistakes

Starting the pointer at 1 instead of 0

Using negative indices incorrectly

The left pointer starts at index 0, the beginning of the list.

2fill in blank

medium

Complete the code to move the right pointer from the end of the list.

DSA Python

right = [1]

Drag options to blanks, or click blank then click option'

A0

Blen(arr)

Clen(arr) - 1

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using len(arr) which is out of range

Starting at 0 which is the first element

The right pointer starts at the last index, which is length minus one.

3fill in blank

hard

Fix the error in the loop condition to continue while left is less than right.

DSA Python

while [1] < right:

Drag options to blanks, or click blank then click option'

Aright - 1

Bright

Cleft + 1

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Using right < right which is always false

Using left + 1 which is incorrect syntax

The loop should run while the left pointer is less than the right pointer.

4fill in blank

hard

Fill both blanks to move pointers correctly: increment left if sum is less, decrement right if sum is more.

DSA Python

if current_sum [1] target:
    left [2] 1

Drag options to blanks, or click blank then click option'

A<

B>

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' in comparison

Using '-=' to move left pointer forward

If the current sum is less than the target, move the left pointer forward by adding 1.

5fill in blank

hard

Fill all three blanks to complete the two pointer sum check: compare, move left, or move right.

DSA Python

if current_sum == target:
    return True
elif current_sum [1] target:
    left [2] 1
else:
    right [3] 1

Drag options to blanks, or click blank then click option'

A<

B+=

C-=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' in comparison instead of '<'

Mixing up '+=' and '-=' for pointers

If current_sum is less than target, move left pointer forward; else move right pointer backward.