Rotate List.cpp

/*
Rotate List
===========

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
*/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution
{
public:
  ListNode *rotateRight(ListNode *head, int k)
  {
    if (!head || !head->next)
      return head;

    auto tail = head;
    int size = 0;
    auto temp = head;
    while (temp)
    {
      size++;
      temp = temp->next;
      if (tail->next)
        tail = tail->next;
    }

    k = k % size;

    if (!k)
      return head;

    ListNode *dummy = new ListNode(-1);
    dummy->next = head;
    temp = dummy;

    for (int i = 0; i < size - k; ++i)
    {
      temp = temp->next;
    }

    head = temp->next;
    temp->next = NULL;
    tail->next = dummy->next;
    return head;
  }
};