题解 | #链表中环的入口结点#

快慢指针 不要边界判断了，就用异常

class Solution:
    def EntryNodeOfLoop(self, pHead):
        if not pHead.next:return pHead.next
        fast,slow = pHead,pHead
        while fast or slow:
            try:
                fast = fast.next.next
                slow = slow.next
                if slow == fast:
                    break
            except:
                return None
        if slow == pHead:return slow
        else:slow = pHead
        while fast or slow:
            fast = fast.next
            slow = slow.next
            if slow == fast:
                return slow