Rotate List

問題描述

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.

思考：用兩個指針A，B，A先走k步，然後A、B同時

想法

• 1、A先走k步，然後A、B同時，直到A到表尾
• 2、head指向B的next；
• 3、將A的next指向表頭，B的next置爲null；

代碼

public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        ListNode first = head;
        ListNode second = head;

        if(head == null || head.next == null)
            return head;

        int sum = 0;

        while(k > 0){
            first = first.next;
            sum++;
            k--;
            if(first == null){
                first = head;
                k = k % sum;
            }

        }

        while(first.next != null){
            first = first.next;
            second = second.next;
            if(second == null)
                second = head;
        }

        first.next = head;
        head = second.next;
        second.next = null;

        return head;
    }
}