[LeetCode]Rotate List

先算出list的长度len，并且处理k，因为k有可能大于len。之后找到倒数第k + 1个节点，双指针即可。之后再重新连起来即可。时间复杂度O(N)，常数空间。代码如下：

	/**
	* 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)return head;
	int len = 0;
	auto curr = head;
	while(curr)
	{
	++len;
	curr = curr->next;
	}
	k %= len;
	if(!k)return head;
	//find the k + 1th to the last
	auto fast = head, slow = head;
	while(k)
	{
	fast = fast->next;
	--k;
	}
	while(fast->next)
	{
	fast = fast->next;
	slow = slow->next;
	}
	//partite and reconnect
	auto newNode = slow->next;
	slow->next = nullptr;
	fast->next = head;
	return newNode;
	}
	};

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