Write a function that moves the last element to the front in a given Singly Linked List. For example, if the given Linked List is 1->2->3->4->5, then the function should change the list to 5->1->2->3->4. Algorithm: Traverse the list till the last node. Use two pointers: one to store the address of the last node and the other for the address of the second last node. After the end of the loop do the following operations.
- Make second last as last (secLast->next = NULL).
- Set next of last as head (last->next = *head_ref).
- Make last as head ( *head_ref = last).
// C Program to move last element to // front in a given linked list #include<stdio.h> #include<stdlib.h> // A linked list node struct Node
{ int data;
struct Node *next;
}; /* We are using a double pointer head_ref here because we change head of the
linked list inside this function.*/
void moveToFront( struct Node **head_ref)
{ /* If linked list is empty, or it
contains only one node, then
nothing needs to be done,
simply return */
if (*head_ref == NULL ||
(*head_ref)->next == NULL)
return ;
/* Initialize second last and
last pointers */
struct Node *secLast = NULL;
struct Node *last = *head_ref;
/*After this loop secLast contains
address of second last node and
last contains address of last node
in Linked List */
while (last->next != NULL)
{
secLast = last;
last = last->next;
}
// Set the next of second last as NULL
secLast->next = NULL;
// Set next of last as head node
last->next = *head_ref;
/* Change the head pointer to
point to last node now */
*head_ref = last;
} // UTILITY FUNCTIONS // Function to add a node at the // beginning of Linked List void push( struct Node** head_ref,
int new_data)
{ // Allocate node
struct Node* new_node =
( struct Node*) malloc ( sizeof ( struct Node));
// Put in the data
new_node->data = new_data;
// Link the old list of the
// new node
new_node->next = (*head_ref);
// Move the head to point to
// the new node
(*head_ref) = new_node;
} /* Function to print nodes in a given linked list */
void printList( struct Node *node)
{ while (node != NULL)
{
printf ( "%d " , node->data);
node = node->next;
}
} // Driver code int main()
{ struct Node *start = NULL;
/* The constructed linked list is:
1->2->3->4->5 */
push(&start, 5);
push(&start, 4);
push(&start, 3);
push(&start, 2);
push(&start, 1);
printf ( "Linked list before moving last to front" );
printList(start);
moveToFront(&start);
printf ( "Linked list after removing last to front" );
printList(start);
return 0;
} |
Output:
Linked list before moving last to front 1 2 3 4 5 Linked list after removing last to front 5 1 2 3 4
Time Complexity: O(n) where n is the number of nodes in the given Linked List.
Auxiliary space: O(1) as it is using constant space
Please refer complete article on Move last element to front of a given Linked List for more details!