题目

 

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;		auto ptr = head;		int length = 0;		while (ptr != nullptr)		{			ptr = ptr->next;			length++;		}        k=k%length;     if(k==0)       return head;		//54321 2		auto newHead = ReverseList(head, length);     if(k==length)       return newHead;		//45321 2		newHead = ReverseList(newHead, k);		//45123 2		int num = k;		auto nextHead = newHead;		while (num > 0)		{			nextHead = nextHead->next;			num--;		}		auto nextNewHead=ReverseList(nextHead, length - k);		auto connPtr = newHead;		while (k > 1)		{			connPtr = connPtr->next;			k--;		}		connPtr->next = nextNewHead;		return newHead;	}	/*   * head 开始结点   * num 翻转的个数   * return 反转后的头结点   */	ListNode* ReverseList(ListNode*head, int num)	{		if (head == nullptr || num == 0)			return nullptr;		auto realTail = head;		ListNode* newHead = nullptr;		ListNode* temp = nullptr;		while (num>0)		{			temp = head->next;			head->next = newHead;			newHead = head;			head = temp;			num--;		}		realTail->next = temp;		return newHead;	}};