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

Approach 1: Two pointers.

Code (Python)

Approach 1:

Code (C++)

Approach 1:

/**
 * 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 || k == 0)
            return head;
        int len = 0;
        ListNode *node = head;
        while (node)
        {
            len++;
            node = node->next;
        }
        k = k % len;
        ListNode *slow = head;
        ListNode *fast = head;
        for (int i = 0; i < k; ++i)
        {
            fast = fast->next;
        }
        while (fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next;
        }
        if (slow != fast)
        {
            fast->next = head;
            head = slow->next;
            slow->next = NULL;
        }
        return head;
    }
};