Description
Q1. Brackets matching – The Delimiters on the Stack (5 marks)
Write a java program that determines whether the given set of delimiters (in our case, it will be
parenthesis such as ( and ) ) is validate or not.
Input:
Your program should read the input set of parenthesis from the user.
Output:
You would write on the console whether a given set of parenthesis is valid or not.
Sample Run:
Enter a String: ()
This is valid
Another run:
Enter a String: )(
This is invalid
Another run:
Enter a String: (())
This is valid
2 ENSF 594
Note: For question 2 and question 3, you can assume that all the expressions contains only single
digits number. There will not be any parenthesis in the expression. The operator will be +, -, * and /.
Q2. Convert from Infix to Postfix (5 marks)
We write expression with an operator (+, -, * and /) places between the operands. This is called infix
notation because operator is placed between the operands. In postfix notation, operator follows the
two operands. For Example A + B becaosme AB+. Below table describe Infix expression to postfix
expression.
Infix Postfix
A + B – C AB+CA * B / C AB*C/
A + B * C AB*C+
A * B + C ABC+*
A * B + C * D AB*CD*+
Below table describe how we can convert an expression from infix to post.
Infix: A + B – C, Postfix: AB+CCharacter Read from Infix
Expression
Infix expression parsed so
far
Postfix Expression Comment
A A A
+ A+ A
B A+B AB
– A+B- AB+ When you see the -,
you can copy the +
to the postfix string
C A+B-C AB+C
End A+B-C AB+C- When you reach at
the end of the
expression, you can
copy the –
Now consider another example
3 ENSF 594
Character Read from Infix
Expression
Infix expression parsed so
far
Postfix Expression Comment
A A A
+ A+ A
B A+B AB
* A+B* AB You cannot copy +
because * has
higher precedence
C A+B*C AB+C When you see the
C, you can copy the
*
A+B*C ABC*
End A+B*C ABC*+ When you see end
of the expression,,
you can copy the +
Below are the input to postfix transition rules:
Item Read from Input Action (infix)
Operand Write it to output
Operator(opThis)
If stack is empty, push opThis
Otherwise, while stack not empty, repeat:
Pop an item
If item is an operator(opTop) and
If opTop < opThis, push opTop
If opTop >= opThis, output opTop
Quit loop if opTOP < opThis
Push opThis
No more items While stack not empty,
Pop item, output it
4 ENSF 594
In the above table, < and >= symbols refers to the operator precedence. The opThis operator has just
been read from the infix input, while opTop operator has just been popped off the stack
You can follow these transition rules in our first two table.
Write a java program that read an infix expression from the user (console), and convert that expression
in the postfix expression.
Sample Run:
Enter infix: 2+3*4
Postfix is: 234*+
Q3. Evaluating expression (4 marks)
Below algorithm describe the evaluating postfix expression
If item read from postfix expression is an operand, then push that item onto the stack
If item read from postfix expression is an operator, pop the top two operands from the stack
and apply the operator to them. Push the result.
When you are done, pop the stack to obtain the answer.
Sample Run:
Enter Postfix: 57+
Evaluates to 12
Submit electronically via D2L:
1. Your source code files. Your TA will run your program to verify that it works correctly. Make sure
your Java program compiles and runs without issues.
2. For Q1, the main file name should be Q1_LastName_FirstName.java. Same pattern will be for Q2
and Q3.
5 ENSF 594
Grading Rubric:
Functionality: produces correct output:
Produce correct output for Q1 (5 marks)
Convert infix expression to postfix ( 5 marks)
Evaluate the expression (4 marks)
Reference:
Some of the contents of the assignment has been adapted from Data Structures and Algorithm in
Java, 2nd Edition by Robert Lafore
Other Source:
Following will be extra resources to read if you are interested.
https://introcs.cs.princeton.edu/java/43stack/
https://eecs.wsu.edu/~nroy/courses/cpts122/labs/Infix2Postfix.pdf
