算法打卡Day8_leetcode _141.环形链表

    //采用快慢双指针
    public boolean hasCycle(ListNode head) {
        if (head == null) {
            return false;
        }
        ListNode fast = head;//快指针，每次走2步
        ListNode slow = head;//慢指针,每次走1步
        while (fast.next != null && fast.next.next != null) {
            fast = fast.next.next;
            slow = slow.next;
            //当快指针赶上慢指针，两指针有重叠时，说明是个环形链表
            if (slow == fast)
                return true;
        }
        return false;
    }