Common linked list patterns (runner technique) in Data Structures Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the slow pointer at the head of the linked list.

Data Structures Theory

slow = [1]

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

Afast

Btail

CNone

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Starting slow at tail or None instead of head.

Confusing slow with fast pointer initialization.

The slow pointer starts at the head of the linked list to begin traversal.

2fill in blank

medium

Complete the code to move the fast pointer two steps ahead in the linked list.

Data Structures Theory

fast = fast[1]next[2]next

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

A.

B->

C=>

D::

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect operators like '->' or '=>' which are not valid in this context.

Moving only one step instead of two.

In many programming languages, the dot operator is used to access the next node in a linked list.

3fill in blank

hard

Fix the error in the loop condition to ensure the fast pointer and its next node are valid.

Data Structures Theory

while fast != None and fast[1]next != None:

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

A=>

B->

C.

D::

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect operators like '->' or '=>' which cause syntax errors.

Not checking fast.next leading to runtime errors.

The dot operator is used to access the 'next' attribute of the fast pointer node.

4fill in blank

hard

Fill both blanks to correctly advance slow by one step and fast by two steps in the loop.

Data Structures Theory

slow = slow[1]next
fast = fast[2]next[3]next

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

A.

B->

C::

D=>

Attempts:

3 left

💡 Hint

Common Mistakes

Using different operators inconsistently.

Advancing fast only one step instead of two.

Use the dot operator to access the next nodes for both slow and fast pointers.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps each node's value to its position if the value is even.

Data Structures Theory

result = [1]: [2] for [3], [1] in enumerate(nodes) if [1] % 2 == 0

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

Aindex

Bvalue

Cfor

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up keys and values in the dictionary comprehension.

Using incorrect loop variable names.

The comprehension maps each value to its index if the value is even. {value: index for index, value in enumerate(nodes) if value % 2 == 0}