06_环形链表

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

# 这个在我的简书 数据结构与算法里有写 利用双指针可以实现


class Solution(object):
    def hasCycle(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        if not head:
            return False

        cur1 = cur2 = head
        while cur2 and cur2.next:
            cur1 = cur1.next
            cur2 = cur2.next.next
            if cur1 == cur2:
                return True
        return False


# leetcode 上最优解 思路一样 快慢指针 上下两个while的条件都对
class Solution2(object):
    def hasCycle(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        if head is None:
            return head
        fast = head
        slow = head
        while fast.next and fast.next.next:
            fast = fast.next.next
            slow = slow.next
            if fast.val == slow.val:
                return True
        return False