Mastering Algorithms with C

Chapter 6. Stacks and Queues

Often it is important to store data so that when it is retrieved later, it is automatically presented in some prescribed order. One common way to retrieve data is in the opposite order as it was stored. For example, consider the data blocks a program maintains to keep track of function calls as it runs. These blocks are called activation records. For a set of functions { f ₁, f ₂, f ₃} in which f ₁ calls f ₂ and f ₂ calls f ₃, a program allocates one activation record each time one of the functions is called. Each record persists until its function returns. Since functions return in the opposite order as they were called, activation records are retrieved and relinquished in the opposite order as they were allocated. Another common way to retrieve data is in the same order as it was stored. For example, this might be useful with a bunch of things to do; often we want to do the first item first and the last item last. Stacks and queues are simple data structures that help in such common situations.

This chapter covers:

Stacks

Efficient data structures for storing and retrieving data in a last-in, first-out, or LIFO, order. This allows us to retrieve data in the opposite order as it was stored.

Queues

Efficient data structures useful for storing and retrieving data in a first-in, first-out, or FIFO, order. This allows us to retrieve data in the same order as it was stored.

Some applications of stacks and queues are:

Semaphores

Programmatic devices for synchronizing ...