题解 | #链表中环的入口结点#

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

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