LeetCode61- rotation list

LeetCode61- rotation list

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1, title

Given a list, the list of rotation, each of the node list to the right by k positions, wherein k is non-negative.
Example:

输入: 1->2->3->4->5->NULL, k = 2
输出: 4->5->1->2->3->NULL
解释:
向右旋转 1 步: 5->1->2->3->4->NULL
向右旋转 2 步: 4->5->1->2->3->NULL

2, thinking

3, Code

c++

class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if(!head) return NULL;
        //计算链表长度
        int n=0;
        for(auto p=head;p;p=p->next)  n++；
        //对k取模
        k%=n;
        auto first=head,second=head;
        //first指针先走K步
        while(k--)    first=first->next;
        //first、second指针同时前进，直到尾部为止
        while(first->next)
        {
            first=first->next;
            second=second->next;
        }
        //first指针指向头结点、secode的下个元素成为头结点，second指针指向null
        first->next=head;
        head=second->next;
        second->next=NULL;
        return head;     
    }
};

Java

class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(!head) return null;
        for(ListNode p=head;p;p=p.next)  n++；
        k%=n;
        ListNode first=head,second=head;
        for(int i=1;i<=k;i++)
        {
            first=first.next;
        }
        
        while(first.next!=null)
        {
            first=first.next;
            second=second.next;
        }
        first.next=head;
        head=second.next;
        second.next=null;
        return head;   
    }
}