1. Queue
Queue – First In / First Out (FIFO) data structure that supports two operations:
push for adding new element at the end of the queue
pop for removing new element at the front of the queue

2. Queue: Push
top
Max
Max
top
Lex
Lex
Nika
Nika
Push
Vlad
Vlad
Joe
Joe

3. Queue: Pop
pop
Max
Max
top
Lex
Lex
Nika
Nika
Vlad
Vlad
Joe
Joe

4. Generic queue Class (STL)
#include <queue>
queue<string> myQueue;
size() returns queue size;
front() returns the front queue element;
push () adds new element to (the end of) the queue;
pop() removes element from (the front of) the queue;

5. Applications
Various lists: print queues, message queues, service request queues, process / thread queues; O(1) push & pop operations.
Round robin: circular queue (front element linked to last.

6. A queue can be implemented with the help of a linked list:
Implementation
A queue can be implemented with the help of a linked list:
front
Max
Lex
Nika
end
Vlad

7. Deque
DEQueue – Double-Ended Queue = stack + queue hybrid, supports adding and removing elements at the front and at the end.
push for adding new element at the end of the queue
pop for removing new element at the front of the queue

8. Deque: Push Joe Joe Max Max Lex Lex Nika Nika Vlad Vlad Jane Jane top
push_front
Joe
top
Max
Max
Lex
Lex
Nika
Nika
push_end
Vlad
end
Vlad
Jane
Jane
end

9. Generic deque Class (STL)
#include <deque>
deque<string> myDeque;
* supports all of the methods of vector and list (including indexes and iterators)
size() returns deque size;
front() returns the front deque element;
back() returns the back deque element;
push_front() - adds new element to the front of the deque;
push_end() - adds new element to the end of the deque;
pop_front() - removes element from the front of the deque;
pop_end() - removes element from the back of the deque;

10. Exercise: Operation Priority
Figure out the priority of operations in an algebraic expression, e.g.
Expression: a*(b+c)-d/e+f
Priority:
Using string and queue
Read expression from cin into a string
Look at each character and if it is +,-,*,/ determine the priority of arithmetic operation
populate the queue with operation in its priority, e.g. (*,2) (+,3) (-,1) (/,3) (+,1)
Print the queue contents

11. Operation Priority Solution
Declare user-defined type: struct OperationPriority { char Operation; int Priority; };
Your queue must store OperationPriority objects
Assign priority levels to operations: 2 for *,/; 1 for +,-
Read expression into string
Set nestingLevel=0
Look at each character
If the character is ‘(‘ then nestingLevel++
If the character is ‘)‘ then nestingLevel--
If the character is ’*’, ’/’ then priority = nestingLevel*2 + 2
If the character is ’+’, ’-’ then priority = nestingLevel*2 +
If the character is ’+’, ’-’, ‘*’, ‘/’ then add it to queue including the priority value
cout the queue

12. Assignment Read chapter 6, prepare for quiz next class.
I will randomly question 10 students. Correct answer earns 1%, incorrect earns -1%.