LeetCode61 Rotate List

题目：

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

For example:
Given

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

and k =

2

,
return

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

.

分析：

利用双指针，一个指针先走k步，然后两个指针同时走，runner走到链表尾时chaser在要翻转之前位置，然后折腾一下指针指向即可。

注意：如果k 大于指针长度时，题目表述不清，应该是按照循环回来处理。所以前面需要求一下链表长度，并把k % size。

代码：

/**
* 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 == nullptr) {
return nullptr;
}
int size = 0;
ListNode* temp = head;
while (temp != nullptr) {
temp = temp -> next;
size++;
}
k = k % size;
ListNode* runner = head;
ListNode* chaser = head;
for (int i = 0; i < k; ++i) {
runner = runner -> next;
}
while (runner -> next != nullptr) {
runner = runner -> next;
chaser = chaser -> next;
}
runner -> next = head;
ListNode* result = chaser -> next;
chaser -> next = nullptr;
return result;
}
};