61. Rotate List

Description

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.

Solution

Two-pointers

由于k可能超出链表长度，所以先得到链表长度然后k对len取模，再进行快慢指针计算。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null || head.next == null || k <= 0) return head;
        
        int len = getLength(head);
        k %= len;
        if (k <= 0) return head;
        
        ListNode slow = head;
        ListNode fast = head;
        while (k-- > 0) {
            fast = fast.next;
        }
        
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        
        ListNode newHead = slow.next;
        fast.next = head;
        slow.next = null;
        return newHead;
    }
    
    public int getLength(ListNode head) {
        int len = 0;
        while (head != null) {
            head = head.next;
            ++len;
        }
        return len;
    }
}