Reverse a Doubly Linked List in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap the next and prev pointers of the current node.

DSA C

void reverse(struct Node** head_ref) {
    struct Node* temp = NULL;
    struct Node* current = *head_ref;
    while (current != NULL) {
        temp = current->[1];
        current->prev = current->next;
        current->next = temp;
        current = current->prev;
    }
}

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

Aprev

Bhead

Cnext

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using current->prev instead of current->next causes incorrect traversal.

Swapping pointers without saving next node leads to losing the list.

We need to store the next pointer of the current node in temp before swapping pointers.

2fill in blank

medium

Complete the code to update the head pointer after reversing the list.

DSA C

if (temp != NULL) {
    *head_ref = temp->[1];
}

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

Anext

Bprev

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to temp->next causes wrong head assignment.

Not updating head leads to unchanged list start.

After the loop, temp points to the last processed node, so head should point to temp->prev.

3fill in blank

hard

Fix the error in the while loop condition to correctly traverse the list.

DSA C

while ([1] != NULL) {
    // swapping pointers
}

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

Acurrent

B*head_ref

Ctemp

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using temp instead of current causes infinite loop or no traversal.

Using *head_ref instead of current causes incorrect condition.

The loop should continue while current is not NULL to traverse all nodes.

4fill in blank

hard

Fill both blanks to correctly swap pointers and move to the next node.

DSA C

temp = current->[1];
current->prev = current->[2];

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

Anext

Bprev

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing prev and next pointers causes incorrect reversal.

Using data instead of pointers causes errors.

We save current->next in temp and assign current->prev to current->next to swap pointers.

5fill in blank

hard

Fill all three blanks to complete the reverse function correctly.

DSA C

void reverse(struct Node** head_ref) {
    struct Node* temp = NULL;
    struct Node* current = *head_ref;
    while (current != NULL) {
        temp = current->[1];
        current->prev = current->[2];
        current->next = temp;
        current = current->[3];
    }
    if (temp != NULL) {
        *head_ref = temp->prev;
    }
}

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

Anext

Bprev

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up prev and next pointers in assignments.

Not moving current correctly causes infinite loop.

We save current->next in temp, assign current->prev to current->next, and move current to current->prev.