The.Algorithm.Design.Manual.Springer-Verlag.1998

Containers
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Containers
Containers are abstract data types that hold stuff. They don't do much more than hold it so that it can be
retrieved later. Still, they are critical to the functioning of society. We will use the term container to
denote a data structure that permits storage and retrieval of data items independently of content. The two
fundamental operations of any container are:
● Put(C,x): Insert a new data item x into the container C.
● Get(C): Retrieve the next item from the container C. Different types of containers support
different retrieval orders, based on insertion order or position.
Containers are typically most useful when they will contain only a limited number of items and when the
retrieval order is predefined or irrelevant. The most popular type of containers are:
● Stacks: Supports retrieval in last in, first out order (LIFO). Stacks are simple to implement, and
very efficient. Indeed, stacks are probably the right container to use when the retrieval order
doesn't matter at all, as when processing batch jobs. The put and get operations for stacks are
usually called push and pop.
● Queues: Supports retrieval in first in, first out order (FIFO). FIFO may seem the fairest way to
control waiting times. However, for many applications, data items have infinite patience. Queues
are trickier to implement than stacks and are appropriate only for applications (like certain
simulations) where the order is important. The put and get operations for queues are usually called
enqueue and dequeue.
● Tables: Supports retrieval by position, so that put and get each accept an index as an argument.
Tables are naturally implemented using arrays.
Each of these containers can be implemented using either arrays or linked lists. With the exception of
tables, the choice of lists versus tables probably doesn't matter very much. The key issue is whether an
upper bound on the size of the container is known in advance, thus permitting a statically allocated array.
Using arrays, put and get can be implemented in constant time per operation for each of the containers.
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