【Leetcode 141】环形链表

环形链表题目

public boolean hasCycle(ListNode head) {
    Set<ListNode> nodesSeen = new HashSet<>();
    while (head != null) {
        if (nodesSeen.contains(head)) {
            return true;
        } else {
            nodesSeen.add(head);
        }
        head = head.next;
    }
    return false;
}

public boolean hasCycle(ListNode head) {
    if (head == null || head.next == null) {
        return false;
    }
    ListNode slow = head;
    ListNode fast = head.next;
    while (slow != fast) {
        if (fast == null || fast.next == null) {
            return false;
        }
        slow = slow.next;
        fast = fast.next.next;
    }
    return true;
}

参考链接
​​​ https://leetcode-cn.com/problems/linked-list-cycle/solution/huan-xing-lian-biao-by-leetcode/​​

扩展拿到环的入口结点
​​​ https://zhuanlan.zhihu.com/p/103626709​​