Reorder Linked List in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to move to the next node in the linked list.

DSA C

current = current->[1];

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

Atail

Bprev

Chead

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to move forward.

Using 'head' or 'tail' which are not pointers of the current node.

In a singly linked list, the pointer to the next node is accessed using 'next'.

2fill in blank

medium

Complete the code to find the middle node of the linked list using slow and fast pointers.

DSA C

while (fast != NULL && fast->[1] != NULL) {
    slow = slow->next;
    fast = fast->next->next;
}

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

Aprev

Bnext

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' for fast pointer movement.

Not checking if fast->next is NULL before accessing fast->next->next.

The fast pointer moves two steps ahead using 'next' pointers to find the middle.

3fill in blank

hard

Fix the error in the code to reverse the second half of the linked list.

DSA C

struct ListNode* prev = NULL;
struct ListNode* curr = head;
while (curr != NULL) {
    struct ListNode* nextTemp = curr->[1];
    curr->next = prev;
    prev = curr;
    curr = nextTemp;
}

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

Anext

Bhead

Ctail

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to save the next node.

Not saving the next node before reversing the link.

To reverse the list, we must store the next node using 'next' pointer before changing links.

4fill in blank

hard

Fill both blanks to merge two halves of the linked list alternately.

DSA C

while (second != NULL) {
    struct ListNode* temp1 = first->next;
    struct ListNode* temp2 = second->[1];
    first->next = second;
    second->next = temp1;
    first = temp1;
    second = [2];
}

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

Anext

Bprev

Ctemp2

Dtemp1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to move forward.

Assigning wrong variable to 'second' causing infinite loop.

We use 'next' to move forward in the second list and assign 'temp2' to second for next iteration.

5fill in blank

hard

Fill all three blanks to complete the reorder list function.

DSA C

void reorderList(struct ListNode* head) {
    if (head == NULL || head->next == NULL) return;

    struct ListNode *slow = head, *fast = head;
    while (fast != NULL && fast->next != NULL) {
        slow = slow->next;
        fast = fast->next->[1];
    }

    struct ListNode* second = slow->next;
    slow->next = NULL;

    struct ListNode* prev = NULL;
    struct ListNode* curr = second;
    while (curr != NULL) {
        struct ListNode* nextTemp = curr->[2];
        curr->next = prev;
        prev = curr;
        curr = nextTemp;
    }

    struct ListNode* first = head;
    second = prev;
    while (second != NULL) {
        struct ListNode* temp1 = first->next;
        struct ListNode* temp2 = second->next;
        first->next = second;
        second->next = temp1;
        first = temp1;
        second = [3];
    }
}

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

Anext

Bprev

Dtemp2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' for fast pointer movement.

Not saving 'next' before reversing links.

Assigning wrong variable to 'second' in merge loop.

Fast pointer moves two steps using 'next', reversing uses 'next', and 'second' moves to 'temp2' to merge.