Problem: 61. 旋转链表

👨‍🏫 力扣官解

/**
 * 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) {
        // 不用动 或 链表少于两个节点
        if(k == 0 || head == null || head.next == null){
            return head;
        }
        int n = 1;// 统计链表的元素个数
        ListNode iter = head;
        while(iter.next != null){
            iter = iter.next;
            n++;
        }
        int offset = n - (k % n);// 从头开始数 offset 个，链表断开
        if(offset == n){
            return head;
        }
        iter.next = head;// 闭链成环
        // 把 iter 移到第 offset 个节点
        while(offset-- > 0){
            iter = iter.next;
        }
        ListNode res = iter.next;
        iter.next = null;// 断环归链
        return res;
    }
}