061 - Rotate List

61. Rotate List

Problem Statement:

Given the head of a linked list, rotate the list to the right by k places.

Example 1:

Input: head = [1,2,3,4,5], k = 2
Output: [4,5,1,2,3]

Example 2:

Input: head = [0,1,2], k = 4
Output: [2,0,1]

Constraints:

• The number of nodes in the list is in the range [0, 500].
• -100 <= Node.val <= 100
• 0 <= k <= 2 * 10⁹

Solution:

Java

public ListNode rotateRight(ListNode head, int k) {
  if (head == null)
    return null;
  int size = 0;
  ListNode temp = head,
      newHead = null,
      p1 = head,
      p2 = head;
  while (temp != null) {
    size++;
    temp = temp.next;
  }
  k %= size;
  for (int i = 0; i < k; i++)
    p2 = p2.next;
  while (p2.next != null) {
    p1 = p1.next;
    p2 = p2.next;
  }
  p2.next = head;
  newHead = p1.next;
  p1.next = null;
  return newHead;
}

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