數據結構：對計算機內存中數據的一種安排。包括：數組、鏈表、棧、二叉樹、哈希表等。
算法：對數據結構中的數據進行各種處理，例如查找特定項，排序等。
解決問題：現實世界中的數據存儲，以前是用索引卡片（一疊卡片）來存儲數據的，現在如果想用計算機來代替索引卡片（凡是用索引卡片的都可以用計算機代替），將會出現一些問題：
• How would you store the data in your computer’s memory? --建模
• Would your method work for a hundred file cards? A thousand? A million? --擴容
• Would your method permit quick insertion of new cards and deletion of old ones?
--插入、刪除
• Would it allow for fast searching for a specified card? --查找
• Suppose you wanted to arrange the cards in alphabetical order. How would you sort them? --排序
程序員的工具
有些數據結構只會在編程語言中用到，而不會被用戶直接使用。
現實世界的建模
數據結構的特性（圍繞查找、增加、刪除的性能）
|
Data Structure |
Data Structure |
Disadvantages |
|
Array |
Quick insertion, very fast access if index known. |
Slow search, slow deletion, fixed size. |
|
Ordered array |
Quicker search than unsorted array. |
Slow insertion and deletion, fixed size |
|
Stack
|
Provides last-in, first-out access. |
Slow access to other items. |
|
Queue |
Provides first-in, first-out access |
Slow access to other items |
|
Linked list |
Quick insertion, quick deletion. |
Slow search.
|
|
Binary tree |
Quick search, insertion, deletion (if tree remains balanced). |
Deletion algorithm is complex.
|
|
Red-black tree |
Quick search, insertion, deletion. Tree always balanced. |
Complex. |
|
2-3-4 tree |
Quick search, insertion, deletion. Tree always balanced. Similar trees good for disk storage. |
Complex. |
|
Hash table |
Very fast access if key known. Fast insertion. |
Slow deletion, access slow if key not known, inefficient memory usage. |
|
Heap |
Fast insertion, deletion, access to largest item. |
Slow access to other items. |
|
Graph |
Models real-world situations. |
Some algorithms are slow and complex. |
抽象數據結構：除了數組之外的數據結構。
算法的概述：插入刪除查找，迭代查詢、排序
Summary
• A data structure is the organization of data in a computer’s memory or in a disk file.
• The correct choice of data structure allows major improvements in program efficiency.
• Examples of data structures are arrays, stacks, and linked lists.
• An algorithm is a procedure for carrying out a particular task.
• In Java, an algorithm is usually implemented by a class method.
• Many of the data structures and algorithms described in this book are most often used to build databases.（數據庫的原理看來不簡單啊）
• Some data structures are used as programmer’s tools: They help execute an algorithm.
• Other data structures model real-world situations, such as telephone lines running between cities.(電話線網和數據結構有什麼關係？也涉及到查詢)
• A database is a unit of data storage composed of many similar records.
• A record often represents a real-world object, such as an employee or a car part.
• A record is divided into fields. Each field stores one characteristic of the object described by the record.
• A key is a field in a record that’s used to carry out some operation on the data.
For example, personnel records might be sorted by a LastName field.
• A database can be searched for all records whose key field has a certain value.
This value is called a search key.索引
關鍵字：當查詢一條記錄時，所使用的那個字段被稱爲(索引)關鍵字。