0061_rotate_list.cc

/**
 * Author: Lanqing Ye
 * Date: 2019-10-01
 */
/* 

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

*/ 

/**
 * 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 head;
        ListNode *pNode = head;
        int listNodeNum = 1;
        while(pNode -> next != nullptr){
            pNode = pNode -> next;
            listNodeNum++;
        }
        k = k % listNodeNum;
        if(k == 0)  return head;
        ListNode *pre =new ListNode(-1);
        pre -> next = head;
        ListNode *pStart = head;
        ListNode *pEnd = head;
        for(int i = 1;i < k;i++){
            pEnd = pEnd -> next;
        }
        while(pEnd -> next != nullptr){
            pEnd = pEnd -> next;
            pre = pre -> next;
            pStart = pStart -> next;
        }
        pre -> next = nullptr;
        pEnd -> next = head;
        return pStart;
        
    }
};