Reverse a Singly Linked List Iterative in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the previous pointer to NULL before starting the reversal.

DSA C

struct Node* reverseList(struct Node* head) {
    struct Node* prev = [1];
    struct Node* current = head;
    struct Node* next = NULL;
    while (current != NULL) {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

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

ANULL

Bhead

Ccurrent

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing prev to head instead of NULL causes incorrect links.

Using uninitialized pointers leads to runtime errors.

We start with prev as NULL because the new tail of the reversed list should point to NULL.

2fill in blank

medium

Complete the code to update the next pointer to the next node in the list inside the loop.

DSA C

while (current != NULL) {
    [1] = current->next;
    current->next = prev;
    prev = current;
    current = next;
}

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

Aprev

Bhead

Ccurrent

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning prev or current instead of next causes loss of list nodes.

Not saving next before changing links breaks the list.

The next pointer stores the next node before changing links, so we don't lose access to the rest of the list.

3fill in blank

hard

Fix the error in the return statement to return the new head of the reversed list.

DSA C

return [1];

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

Acurrent

Bprev

Chead

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Returning head returns the original list, not reversed.

Returning current or next leads to NULL or incomplete list.

After the loop, prev points to the new head of the reversed list, so we return prev.

4fill in blank

hard

Fill both blanks to complete the while loop condition and update current pointer correctly.

DSA C

while ([1] != NULL) {
    next = current->next;
    current->next = prev;
    prev = current;
    current = [2];
}

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

Acurrent

Bprev

Cnext

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev in the loop condition causes infinite loop.

Updating current to prev or head breaks traversal.

The loop continues while current is not NULL, and current moves forward by assigning it to next.

5fill in blank

hard

Fill all three blanks to complete the iterative reversal function correctly.

DSA C

struct Node* reverseList(struct Node* head) {
    struct Node* prev = [1];
    struct Node* current = head;
    struct Node* next = NULL;
    while (current != [2]) {
        next = current->next;
        current->next = [3];
        prev = current;
        current = next;
    }
    return prev;
}

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

ANULL

Bhead

Cprev

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of NULL for prev initialization.

Wrong loop condition causes infinite or no loop.

Setting current->next to wrong pointer breaks the list.

Initialize prev to NULL, loop while current is not NULL, and set current->next to prev to reverse the link.