环形链表 II

class ListNode:
    def __init__(____):
        self.val = val
        self.next = next

def solve():
    def detectCycle(____):
        slow = fast = head
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                slow = head
                while slow != fast:
                    slow = slow.next
                    fast = fast.next
                return slow
        return None
    head = ListNode(____)
    node2 = ListNode(____)
    node0 = ListNode(____)
    node4 = ListNode(____)
    head.next = node2
    node2.next = node0
    node0.next = node4
    node4.next = node2
    result = detectCycle(____)
    print(____)