Java 代码实现链表节点每 K 个一组翻转

public ListNode reverseKGroup(ListNode head, int k) {
    ListNode dummy = new ListNode(0);
    dummy.next = head;
    ListNode prev = dummy;
    ListNode curr = head;
    int count = 0;

    while (curr != null) {
        count++;
        if (count % k == 0) {
            // 翻转当前组
            prev = reverse(prev, curr.next);
            curr = prev.next;
        } else {
            curr = curr.next;
        }    
    }

    return dummy.next;
}

// 翻转prev->n1->...->nk->next为prev->nk->...->n1->next
private ListNode reverse(ListNode prev, ListNode next) {
    ListNode last = prev.next; // 记录翻转后的最后一个节点
    ListNode curr = last.next;

    while (curr != next) {
        last.next = curr.next;
        curr.next = prev.next;
        prev.next = curr;
        curr = last.next;
    }

    return last;
}