61. 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.

1. 

/**
 * 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 || !k || !head->next)
            return head;
        ListNode *p, *q=head, *r;
        int l=0, i;
        for(p=head; p; p=p->next)
            l++;
        k = k%l;
        for(i=0; i<k; i++)
        {
            if(!q->next)
                q = head;
            else
                q = q->next;
        }
        p=head;
        while(q->next)
        {
            p = p->next;
            q = q->next;
        }
        r = p->next;
        if(!r)
            return head;
        p->next = NULL;
        q->next = head;
        return r;
    }
};

 

2.

先连成环，算长度。

/**
 * 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 || !k)
            return head;
        ListNode *p, *q=head, *r;
        int l=1, i;
        for(p=head; p->next; p=p->next)
            l++;
        p->next = head;
        k = l-k%l;
        for(i=0; i<k; i++)
            p = p->next;
        head=p->next;
        p->next=NULL;
        return head;
    }
};