Question

The following C function takes a singly-linked list of integers as a parameter and rearranges the elements of the list. The function is called with the list containing the integers 1,2,3,4,5,6,7 in the given order. What will be the contents of the list after the function completes execution?

struct node { int value; struct node *next; };
void rearrange(struct node *list) {
  struct node *p, *q; int temp;
  if (!list || !list->next) return;
  p = list; q = list->next;
  while (q) {
    temp = p->value; p->value = q->value;
    q->value = temp; p = q->next;
    q = p ? p->next : 0;
  }
}

Accepted Answer

The correct answer is (B) 2,1,4,3,6,5,7. Tracing: p=node1,q=node2 → swap values (node1↔node2 become 2,1). p=node3,q=node4 → swap (become 4,3). p=node5,q=node6 → swap (become 6,5). p=node7,q=NULL (node7 has no next) → loop ends. Final: 2,1,4,3,6,5,7.

Explanation