61. Rotate List

• Difficulty: Medium

• Topics: Linked List, Two Pointers

• Similar Questions:

  • Rotate Array

  • Split Linked List in Parts

Problem:

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

Solutions:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (head == NULL)   return NULL;
        int count = 1;
        ListNode* cur = head;

        while (cur->next) {
            ++count;
            cur = cur->next;
        }
        cur->next = head;

        k = k % count;

        cur = head;
        for (int i = 0; i < (count - k - 1); ++i) {
            cur = cur->next;
        }

        ListNode* ret = cur->next;
        cur->next = NULL;
        return ret;

    }
};