反转链表-迭代

def solve():
    class ListNode:
        def __init__(____):
            self.val = val
            self.next = next
    
    # 创建链表 ____->____->____->____->____
    head = ListNode(____)
    head.next = ListNode(____)
    head.next.next = ListNode(____)
    head.next.next.next = ListNode(____)
    head.next.next.next.next = ListNode(____)
    
    # 迭代反转
    prev = None
    curr = head
    while curr:
        next_node = curr.next
        curr.next = prev
        prev = curr
        curr = next_node
    
    # 输出反转后的链表
    result = []
    while prev:
        result.append(str(____))
        prev = prev.next
    print('____'.join(____))