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 <bits/stdc++.h> using namespace std;
// A linked list node class Node
{ public :
int data;
Node *next;
}; /* We are using a double pointer head_ref here because we change
head of the linked list inside
this function.*/
void moveToFront(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 */
Node *secLast = NULL;
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(Node** head_ref,
int new_data)
{ // Allocate node
Node* new_node = new Node();
// Put in the data
new_node->data = new_data;
// Link the old list off 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(Node *node)
{ while (node != NULL)
{
cout << node->data << " " ;
node = node->next;
}
} // Driver code int main()
{ 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);
cout <<
"Linked list before moving last to front" ;
printList(start);
moveToFront(&start);
cout <<
"Linked list after removing last to front" ;
printList(start);
return 0;
} // This code is contributed by rathbhupendra |
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) because using constant variables
Please refer complete article on Move last element to front of a given Linked List for more details!