Data Structure Questions and Answers – Singly Linked List Operations – 3

This set of Data Structure Questions and Answers for Experienced people focuses on “Singly Linked Lists Operations – 3”.

1. The following function reverse() is supposed to reverse a singly linked list. There is one line missing at the end of the function.

/* Link list node */
struct node
{
    int data;
    struct node* next;
};
 
/* head_ref is a double pointer which points to head (or start) pointer 
  of linked list */
static void reverse(struct node** head_ref)
{
    struct node* prev   = NULL;
    struct node* current = *head_ref;
    struct node* next;
    while (current != NULL)
    {
        next  = current->next;  
        current->next = prev;   
        prev = current;
        current = next;
    }
    /*ADD A STATEMENT HERE*/
}

What should be added in place of “/*ADD A STATEMENT HERE*/”, so that the function correctly reverses a linked list.
a) *head_ref = prev;
b) *head_ref = current;
c) *head_ref = next;
d) *head_ref = NULL;
View Answer

2. What is the output of following function for start pointing to first node of following linked list?

1->2->3->4->5->6
void fun(struct node* start)
{
    if(start == NULL)
    return;
    printf("%d  ", start->data); 
    if(start->next != NULL )
    fun(start->next->next);
    printf("%d  ", start->data);
}

a) 1 4 6 6 4 1
b) 1 3 5 1 3 5
c) 1 2 3 5
d) 1 3 5 5 3 1
View Answer

3. The following C function takes a simply-linked list as an input argument. It modifies the list by moving the last element to the front of the list and returns the modified list. Some part of the code is left blank. Choose the correct alternative to replace the blank line.

typedef struct node 
{
    int value;
    struct node *next;
}Node;
 
Node *move_to_front(Node *head) 
{
    Node *p, *q;
    if ((head == NULL: || (head->next == NULL)) 
    return head;
    q = NULL; p = head;
    while (p-> next !=NULL) 
    {
        q = p;
        p = p->next;
    }
   _______________________________
  return head;
}

a) q = NULL; p->next = head; head = p;
b) q->next = NULL; head = p; p->next = head;
c) head = p; p->next = q; q->next = NULL;
d) q->next = NULL; p->next = head; head = p;
View Answer

4. The following C function takes a single-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;
    }
}

a) 1, 2, 3, 4, 5, 6, 7
b) 2, 1, 4, 3, 6, 5, 7
c) 1, 3, 2, 5, 4, 7, 6
d) 2, 3, 4, 5, 6, 7, 1
View Answer

5. In the worst case, the number of comparisons needed to search a singly linked list of length n for a given element is?
a) log 2 n
b) ⁿ⁄₂
c) log 2 n – 1
d) n
View Answer

6. Given pointer to a node X in a singly linked list. Only one pointer is given, pointer to head node is not given, can we delete the node X from given linked list?
a) Possible if X is not last node
b) Possible if size of linked list is even
c) Possible if size of linked list is odd
d) Possible if X is not first node
View Answer

    struct node *temp  = X->next;
    X->data  = temp->data;
    X->next  = temp->next;
    free(temp);

7. You are given pointers to first and last nodes of a singly linked list, which of the following operations are dependent on the length of the linked list?
a) Delete the first element
b) Insert a new element as a first element
c) Delete the last element of the list
d) Add a new element at the end of the list
View Answer

8. In the worst case, the number of comparisons needed to search a singly linked list of length n for a given element is?
a) log2 n
b) ⁿ⁄₂
c) log2 n – 1
d) n
View Answer

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