# 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;
}
};