5.8. Stacks¶
5.8.1. Stack Terminology and Implementation¶
The stack is a list-like structure in which elements may be inserted or removed from only one end. While this restriction makes stacks less flexible than lists, it also makes stacks both efficient (for those operations they can do) and easy to implement. Many applications require only the limited form of insert and remove operations that stacks provide. In such cases, it is more efficient to use the simpler stack data structure rather than the generic list. For example, the freelist is really a stack.
Despite their restrictions, stacks have many uses. Thus, a special vocabulary for stacks has developed. Accountants used stacks long before the invention of the computer. They called the stack a “LIFO” list, which stands for “Last-In, First-Out.” Note that one implication of the LIFO policy is that stacks remove elements in reverse order of their arrival.
The accessible element of the stack is called the top element.
Elements are not said to be inserted, they are pushed
onto the stack.
When removed, an element is said to be popped from the
stack.
Here is a simple stack ADT.
As with lists, there are many variations on stack implementation. The two approaches presented here are the array-based stack and the linked stack, which are analogous to array-based and linked lists, respectively.
5.8.1.1. Array-Based Stacks¶
Here is a complete implementation for the array-based stack class.
The array-based stack implementation is essentially a simplified version of the array-based list. The only important design decision to be made is which end of the array should represent the top of the stack.
