61. Rotate List

Given a list, rotate the list to the right by k places, where k is non-negative.


Example:

Given 1->2->3->4->5->NULL and k = 2,

return 4->5->1->2->3->NULL.

 

Since n may be a large number compared to the length of list. So we need to know the length of linked list.After that, move the list after the (l-n%l )th node to the front to finish the rotation.

Ex: {1,2,3} k=2 Move the list after the 1st node to the front

Ex: {1,2,3} k=5, In this case Move the list after (3-5%3=1)st node to the front.

So the code has three parts.

1. Get the length

2. Move to the (l-n%l)th node

3)Do the rotation

public ListNode rotateRight(ListNode head, int n) {
    if (head==null||head.next==null) return head;
    ListNode dummy=new ListNode(0);
    dummy.next=head;
    ListNode fast=dummy,slow=dummy;

    int i;
    for (i=0;fast.next!=null;i++)//Get the total length 
    	fast=fast.next;
    
    for (int j=i-n%i;j>0;j--) //Get the i-n%i th node
    	slow=slow.next;
    
    fast.next=dummy.next; //Do the rotation
    dummy.next=slow.next;
    slow.next=null;
    
    return dummy.next;
}