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.

Have you met this question in a real interview?

 

Analysis:

Assume the length of the list is len, we need to consider the situation that k > len which means to rotate the right k%n steps. Since rotate operation is a kind of circling operation. We first count the length of the list, and connect end to head to make the list as a circle. Then, we only need to move forward by len-k%len steps to reach the new end of the list. Now the next node is the new head.

 

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int n) {
        if (head==null || head.next==null) return head;
    
        ListNode end = null;
        int len = 1;
        end = head;
        while (end.next!=null){
            end = end.next;
            len++;
        }
        end.next = head;
        int step = len - n%len;
        int index = 1;
        end = head;
        while (index<step){
            end = end.next;
            index++;
        }
        head = end.next;
        end.next = null;
        return head;              
    }
}