LeetCode:Rotate List

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.

 

 思路：先遍历一遍，得出链表长度，注意k可能大于len令k%=len，将尾节点next指针指向首节点,形成一个环 ，然后接着跑len-k步， 从这里断开，就是要求的结果。

/**
 * 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 || k==0) return head;
        
        int len=1;
        ListNode *p=head;
        while(p->next)
        {
            len++;
            p=p->next;
        }
        
        int step=len-k%len;
        
        p->next=head;//尾节点next指针指向首节点
        //向后走step步 然后断开
        
        for(int i=0;i<step;i++)
            p=p->next;
        
        head=p->next;
        p->next=NULL;
        
        return head;
    }
};