1ADS Lecture 11

Stacks contd.

ADS Lecture 11 3

Singly Linked list-based Stack•Top of stack is head of list (can insert elements at head in constant time, at tail in linear time)•To perform operation size in constant time, keep track of size via instance variable• Implement generic stack using generic linked list

e1 e2 e3 e4 nullhead

e2 e3 e4 nullhead

e5 e2 e3 e4 nullhead

pop()

push(e5)

A Generic NodeStack Class

ADS Lecture 114

• Code given in next few slides • All methods are executed in constant time (except toString)

• In addition, space requirement is O(n), where n is current number of elements in stack

• Do not need a new exception to be created to handle overflow problems

• Use instance variable top to refer to head of list (null if list empty)

• To push new element e onto stack simply add to head of list, to pop simply remove head and return its element

NodeStack<E>

Node<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

NodeStack<E>

recursive

NodeStack<E>

recursive

Test

Test

Another example of using a stack… a (simple integer) Reverse Polish Calculator

Random fact #5

Random fact #5

In 1973, amongst physicist, computer scientists, …, the HP35was the “must have” item. It was cool, exotic (first commercial rpn calculator),and most importantly … it felt good!

“Felt good”? … the keys had a “click”, i.e. a push and then “click” like a micro switch. Really beautiful.

It cost me 1 month’s pay (about £70 as a student in 1973)

end of random fact #5

RPN Calculator

RPN Calculator

RPN Calculator

Use java Stack<String>

RPN Calculator

Use Stack methods as advertised

RPN Calculator

for each

RPN Calculator

User entered some data as a String. If input String is an integer push it onto the stack S

Cool code

RPN Calculator

RPN Calculator

NOTE: no exception handling in event of stack overflow or underflow

What is “overflow” and what is “underflow”?