Detect if a Linked List is Circular in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA C

struct Node* slow = [1];

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

ANULL

Bhead

Cslow

Dfast

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing slow to NULL will cause no traversal.

Using fast instead of head mixes pointer roles.

The slow pointer should start 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 safely.

DSA C

fast = fast->next->[1];

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

Anext

Bprev

Chead

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' is invalid in singly linked lists.

Accessing 'data' instead of 'next' causes errors.

To move two steps ahead, access next of next node using fast->next->next.

3fill in blank

hard

Fix the error in the loop condition to check if fast and fast->next are not NULL.

DSA C

while (fast != NULL && fast->[1] != NULL) {

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

Aprev

Bdata

Cnext

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'prev' causes compilation errors in singly linked lists.

Checking 'data' is meaningless for pointer safety.

We must check fast->next to ensure the fast pointer can move two steps safely.

4fill in blank

hard

Fill both blanks to update slow and fast pointers correctly inside the loop.

DSA C

slow = slow->[1];
fast = fast->[2]->next;

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

Anext

Bprev

Chead

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' in singly linked lists causes errors.

Using 'data' instead of 'next' breaks pointer logic.

Both slow and fast pointers move forward using the 'next' pointer.

5fill in blank

hard

Fill all three blanks to return true if the list is circular, else false.

DSA C

if (slow == [1]) {
    return [2];
} else {
    return [3];
}

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

Afast

Btrue

Cfalse

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Returning false when pointers meet is wrong.

Comparing slow to head instead of fast misses the cycle.

If slow meets fast, the list is circular (return true), else return false.