61. Rotate List (Medium)

https://leetcode.com/problems/rotate-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

Hints

Solutions

/**
 * 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;
        }

        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode fast = dummy, slow = dummy;
        int len;
        // Get the total length of the list
        for (len = 0; fast.next != null; len++) {
            fast = fast.next;
        }
        // Get the (len - k%len)th node
        for (int j = len - (k % len); j > 0; j--) {
            slow = slow.next;
        }

        // Rotate the list
        fast.next = dummy.next;
        dummy.next = slow.next;
        slow.next = null;

        return dummy.next;
    }
}
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