题目

the leetcode link

解题思路

  1. 计算链表长度，同时初始化哈希索引
  2. 取余去重
  3. 形成环，链尾指向链头
  4. 定位到翻转后的尾结点
  5. 断链
  6. 返回新链头

    代码

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null) return head;

        //哈希索引存储
        Map<Integer,ListNode> map  = new HashMap<>();
        ListNode cur = head;
        int len = 1;
        //计算链表长度， 同时初始化哈希索引
        while(cur.next != null){
            map.put(len++, cur);
            cur =cur.next;
        }

        //去重，转n*len+k次，等价于转k%len次，k%len=0等价与0次翻转
        if((k=(k%len))==0) return head;

        //形成环
        cur.next = head;

        //找到翻转后的尾结点
        ListNode newTail = map.get(len-k);

        //断开头尾
        ListNode newHead = newTail.next;
        newTail.next = null;

        //返回头节点
        return newHead;
    }
}