Rotate a Linked List Java Program - The Coding Shala

Home >> Interview Questions >> Rotate a linked list

Rotate a Linked List

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



Example 1:

Input: 1->2->3->4->5->NULL, k = 2

Output: 4->5->1->2->3->NULL

Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL

Example 2:
Input: 0->1->2->NULL, k = 4
Output: 2->0->1->NULL
Explanation:
rotate 1 steps to the right: 2->0->1->NULL
rotate 2 steps to the right: 1->2->0->NULL
rotate 3 steps to the right: 0->1->2->NULL
rotate 4 steps to the right: 2->0->1->NULL

Rotate a Linked List Java Program

Approach 1:
Add tail to head and move new pointer to len - k%len length.

Java Code 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null || head.next == null) return head;
        int len = 1;
        ListNode newHead = head;
        while(newHead.next != null){
            len++;
            newHead = newHead.next;
        }
        k = len-(k%len);
        newHead.next = head;
        while(k-- > 1) head = head.next;
        newHead = head.next;
        head.next = null;
        return newHead;
    }
}



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