[LeetCode] 61 Rotate List，leetcoderotate

[LeetCode] 61 Rotate List，leetcoderotate

   
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.
 

解題思路：

雙指針（tail，pre）找到鏈表的尾部和總長度，使用pre走 （len-k%(len)-1) 長度到達要修改的尾部點進行修改

/**
 * 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||head->next==NULL)return head;
        ListNode *tail,*pre;
        tail=pre=head;
        int len=1;
        while(tail->next!=NULL) //找到尾部
        {
            tail=tail->next;
            len++;
        }
        int i=len-(k%(len))-1;  //考慮k數據的過大
        while(i>0)
        {
            i--;
            pre=pre->next;
        }
        tail->next=head;
        head=pre->next;
        pre->next=NULL;
        return head;
    }
};