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

Explanation: *head_ref = prev; At the end of while loop, the prev pointer points to the last node of original linked list.

We need to change *head_ref so that the head pointer now starts pointing to the last node.

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

Explanation: fun() prints alternate nodes of the given Linked List, first from head to end, and then from end to head.

If Linked List has even number of nodes, then skips the last node.

3. The following C function takes a simply-linked list as 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

Explanation: None.

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

Explanation: The function rearrange() exchanges data of every node with its next node. It starts exchanging data from the first node itself.

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

Explanation: In the worst case, the element to be searched has to be compared with all elements of linked list.

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

Explanation:

Following are simple steps.

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

Explanation: a) Can be done in O(1) time by deleting memory and changing the first pointer.

b) Can be done in O(1) time, see push() here

c) Delete the last element requires pointer to previous of last, which can only be obtained by traversing the list.

d) Can be done in O(1) by changing next of last and then last.

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

Explanation: Maximum number used in case of worst case.

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