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GO Classes DPP | GATE CS | Data Structures | Delete Last Node

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7 7 votes

Consider the following C function intended to delete the last node of a singly linked list:

void removeLast(struct Node *head) {
    struct Node *p = head;
    struct Node *q = p->next;

    while (q->next != NULL) {
        p = q;
        q = q->next;
    }

    p->next = NULL;
    free(q);
}

For which linked lists does this function work correctly?

  1. No linked lists
     
  2. All non-empty linked lists
     
  3. All linked lists with more than one node
     
  4. Empty list and all linked lists with more than one node
     
  5. All linked lists

4 Answers

1 1 vote

If the list is empty, $\texttt{head == NULL}$, so $\texttt{p->next}$ causes invalid access.

If the list has one node, then $\texttt{q = p->next}$ becomes $\texttt{NULL}$, so $\texttt{q->next}$ causes invalid access.

For lists with more than one node, $\texttt{p}$ reaches the second-last node and $\texttt{q}$ reaches the last node. 

Then $\texttt{p->next = NULL}$ removes the last node correctly.

Answer : C

0 0 votes
Answer: C. All linked lists with more than one node, because empty list and list with one node causes invalid access, but more than one node causes no problems.
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