00015

力扣 142 环形链表

class Solution:
    def detectCycle(self, head: Optional[ListNode]) -> Optional[ListNode]:
        left = head
        fast = head
        while fast and fast.next:
            fast = fast.next.next
            left = left.next
            if fast == left:
                temp = head
                while temp != left:
                    temp = temp.next
                    left = left.next
                return temp
        return None