The Self-Taught Computer Scientist

stack: An abstract data type and a linear data structure that allows you to remove only the most 
recent element you added.
last in, first out data structure: A data structure where the last item you put into the data structure 
is the first item to come out of it.
limited- access data structure: A type of data structure that forces you to access its information in 
a particular order.
pushing: Putting a new item onto a stack.
popping: Removing the last item from a stack.
peeking: Looking at the top element in a stack without removing it.
bounded stack: A stack that limits how many items you can add to it.
unbounded stack: A stack that does not limit how many items you can add to it.
Challenges
1. 
Modify your balanced string program to check whether both parentheses, 
()
, and brackets, 
{}
, 
are balanced in a string.
2. 
Design a max stack that allows you to push, pop, and keep track of your stack’s biggest number 
in O(1) time.

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12
Queues
All students should have the opportunity to learn how to program. Computer science is the basis for 
modern day creativity and expression. The computer programmers of tomorrow will revolu-
tionize medicine.
Anne Wojcicki
A queue is an abstract data type and a linear data structure where you can add items only to the 
rear and remove them from the front (Figure 12.1). The queue abstract data type describes a data 
structure that works like the checkout lines at a grocery store: the first person in the line is the first 
person to check out, and newcomers join the line’s rear.
A queue is an example of a first- in, first- out (FIFO) data structure. As the name implies, in a first- in,