Data comes in all shapes and sizes, but often it can be organized in the same way. For example, consider a list of things to do, a list of ingredients in a recipe, or a reading list for a class. Although each contains a different type of data, they all contain data organized in a similar way: a list. A list is one simple example of a data structure. Of course, there are many other common ways to organize data as well. In computing, some of the most common organizations are linked lists, stacks, queues, sets, hash tables, trees, heaps, priority queues, and graphs, all of which are discussed in this book. Three reasons for using data structures are efficiency, abstraction, and reusability.