leetcode25.k个一组翻转链表

思路源自

【力扣hot100】【LeetCode 25】k个一组翻转链表｜虚拟节点的应用

 

/**
 * 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 reverseKGroup(ListNode head, int k) {
        ListNode dummyHead = new ListNode(0, head);
        ListNode cur = dummyHead;
        while (true) {
            ListNode groupPre = cur;
            int kth = k;
            while (cur != null && kth > 0) {
                cur=cur.next;
                kth--;
            }
            if (cur == null) {
                break;
            } else {
                ListNode groupNext = cur.next;
                cur = groupPre.next;
                ListNode pre = groupNext;
                while (cur != groupNext) {
                    ListNode temp = cur.next;
                    cur.next = pre;
                    pre=cur;
                    cur = temp;
                }
                cur = groupPre.next;
                groupPre.next = pre;
            }
        }
        return dummyHead.next;
    }
}