Rotate List

LeetCode Q 61 - 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

Solution

Code:

public ListNode rotateRight(ListNode head, int k) {
	if (head == null || head.next == null || k == 0)
		return head;
	
	int len = 1;

	ListNode tail = head;
	while (tail.next != null) {
		len++; tail = tail.next;
	}

	if (k % len == 0) return head;

	k %= len;

	ListNode dummy = new ListNode(-1); dummy.next = head;
	ListNode curr = head;
	for (int i = 1; i < len - k; i++) {
		curr = curr.next;
	}

	tail.next = dummy.next;
	dummy.next = curr.next;
	curr.next = null;

	return dummy.next;
}