061 Rotate List [Leetcode]

题目内容：

Given a list, rotate the list to the right by k places, where k is non-negative.

For example:

Given 1->2->3->4->5->NULL and k = 2,

return 4->5->1->2->3->NULL.

思路：

使用双指针。注意处理k比链表长度还要大的情况。

/**
* 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;

ListNode *pre = head, *tail(NULL), *newHead(NULL);
int len(1);
while(pre->next != NULL) {
++len;
pre = pre->next;
}

k %= len;
if(len == 1 || k == 0)
return head;

tail = pre;
pre = head;
for(int i = 0; i < len - k - 1; ++i) {
pre = pre->next;
}
newHead = pre->next;
pre->next = NULL;
tail->next = head;

return newHead;
}
};