题解 | #链表中的节点每k个一组翻转#

class Solution:
    def reverseKGroup(self, head: ListNode, k: int) -> ListNode:
        pre = res = ListNode(0)
        cur = head
        while cur:
            stack = []
            tmp = cur
            for _ in range(k):
                if cur:
                    stack.append(cur.val)
                    cur = cur.next
            if len(stack) == k:
                while stack:
                    pre.next = ListNode(stack.pop())
                    pre = pre.next
            else:
                pre.next = tmp
        return res.next