如何使用Python实现链表的交换相邻k个节点操作

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def swap_k_nodes(head: ListNode, k: int) -> ListNode:
    if not head or not head.next or k == 1:
        return head
    dummy = ListNode(0)
    dummy.next = head
    pre = dummy
    cur = head
    cnt = 0
    while cur:
        cnt += 1
        if cnt % k == 0:
            pre = reverse(pre, cur.next)
            cur = pre.next
        else:
            cur = cur.next
    return dummy.next

def reverse(pre: ListNode, end: ListNode) -> ListNode:
    cur = pre.next
    nxt = cur.next
    while nxt != end:
        cur.next = nxt.next
        nxt.next = pre.next
        pre.next = nxt
        nxt = cur.next
    return cur

# 测试代码
input_node = ListNode('p')
input_node.next = ListNode('i')
input_node.next.next = ListNode('d')
input_node.next.next.next = ListNode('a')
input_node.next.next.next.next = ListNode('n')
input_node.next.next.next.next.next = ListNode('c')
input_node.next.next.next.next.next.next = ListNode('o')
input_node.next.next.next.next.next.next.next = ListNode('d')
print('Before swap: ', end='')
print_linked_list(input_node)
output_node = swap_k_nodes(input_node, 3)
print('After  swap: ', end='')
print_linked_list(output_node)

Before swap: p -> i -> d -> a -> n -> c -> o -> d -> None
After  swap:  d -> i -> p -> a -> n -> c -> o -> d -> None