创建单链表；在单链表上查找第i个数据结点，返回其data值；在单链表第i个位置上插入一个取值为value的新的数据结点；删除单链表第i个数据结点，并返回该数据结点的取值；求单链表的长度。-Create a single list　in a single list on the first i find a data node, return the data value　in a single list on the first i positions to insert a value for the value of the new data node　to delete a single list of data i-node point, and returns the value of the data node　find the length of a single list.