题解 | #链表中环的入口结点#

/**
     * 用hashMap保存下个节点的前驱节点，当key有多个前驱节点就是入口
     *
     * @param pHead
     * @return
     */
    public static ListNode EntryNodeOfLoop(ListNode pHead) {
        Map<ListNode, ListNode> map = new HashMap<>();
        if (pHead == null || pHead.next == null) {
            return null;
        }
        ListNode next = pHead;
        while (next != null) {
            if (map.get(next.next) == null) {
                map.put(next.next, next);
            } else {
                if (next != pHead) {
                    return next.next;
                } else {
                    return next;
                }
            }
            next = next.next;
        }
        return null;
    }