Two-pointer technique in Data Structures Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize two pointers at the start and end of the list.

Data Structures Theory

left = 0
right = [1]

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

Alen(arr) - 1

B0

Clen(arr)

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting right pointer to len(arr) causes index out of range error.

Setting right pointer to 0 makes both pointers start at the same position.

The right pointer should start at the last index, which is len(arr) - 1.

2fill in blank

medium

Complete the code to move the left pointer one step to the right.

Data Structures Theory

left = left [1] 1

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

A-

B+

C*

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' moves the pointer left instead of right.

Using '*' or '//' does not correctly move the pointer by one step.

To move the left pointer right, add 1 to its current position.

3fill in blank

hard

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

Data Structures Theory

while left [1] right:
    # process elements

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

A<=

B>

C>=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' or '<=' causes the pointers to overlap or cross incorrectly.

Using '>' reverses the logic and may cause the loop to never run.

The loop should run while left < right to avoid pointers crossing.

4fill in blank

hard

Fill both blanks to correctly move the pointers towards each other.

Data Structures Theory

left = left [1] 1
right = right [2] 1

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

A+

B-

C*

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' for left pointer moves it left instead of right.

Using '+' for right pointer moves it right instead of left.

The left pointer moves right by adding 1, and the right pointer moves left by subtracting 1.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each word to its length if length is greater than 3.

Data Structures Theory

result = [1]: [2] for word in words if len(word) [3] 3

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

Aword

Blen(word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' filters wrong words.

Swapping keys and values causes incorrect dictionary structure.

The dictionary keys are words, values are their lengths, and the condition filters words longer than 3 characters.