【LeetCode】Rotate List 解题报告

【题目】

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

.
【解析】
题意：把链表循环右移k个结点。

不是很难，主要是几个易错点：1）k 可能大于等于链表长度！！！2）链表为空或长度为1。

/**
 * 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 || n < 1) return head;
        
        //遍历链表求其长度，并找到尾部
        ListNode node = head;
        ListNode tail = null;
        ListNode newhead = null;
        int len = 0;
        while (node != null) {
            len++;
            tail = node;
            node = node.next;
        }
        
        //只有一个结点时，返回原链表即可
        if (len == 1 || n % len == 0) return head;
        
        //把链表首位拼接
        tail.next = head;
        
        //找到右移后的链表尾部
        node = head;
        int i = 1;
        while (i != len - n % len) {
            i++;
            node = node.next;
        }
        newhead = node.next;
        node.next = null;
        
        return newhead;
    }
}