在O（1）时间内删除链表节点（剑指offer_18.1）

public ListNode deleteNode(ListNode head,ListNode tobeDelete)
{
    if(head == null || tobeDelete == null)
    {
        return null;
    }
    if(tobeDelete.next != null)
    {
        //要删除的节点不是尾结点
        ListNode next = tobeDelete.next;
        tobeDelete.val = next.val;
        tobeDelete.next = next.next;
    }else{
        if(head == tobeDelete)
        {
            head = null;
        }
        else
        {
            ListNode cur = head;
            while(cur.next != null)
            {
                 cur = cur.next;
            }
            cur.next = null;
        }
    }
    return head;
}