数据结构的主要任务就是通过描述对象的结构特征，包括逻辑结构在内的联系，然后把逻辑结构表示成计算机可实现的物理结构，从而方便计算机处理(Linked_List:The formal definition is "a data structure consisting of a group of nodes which together represent a sequence." Like arrays,linked lists have indexes,but are accessed by iterators.In the linked list below,the head is "12",which is where the iterator always begins.Suppose we have a linked list object called "list",then list.head = 12 and list.head.next = 99.The last node is called the tail and is always "null" (nothing there).)