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CPSC 331: HW3
HW3

This assignment will be marked out of 30 points. You also have an opportunity to earn 5 bonus
points. This is an individual assignment. Please review the rules on academic misconduct on the
course D2L page.
This assignment consists of two parts. The first part consists of problems that will give you
more practice working with binary trees. The second part consists of a coding exercise that explores
the use of trees in parsing and evaluating arithmetic expressions.
Part I
1. (5 points)
Prove the following:
• A binary tree with n nodes has n + 1 null links.
• In a non-empty binary tree, the number of full nodes plus one is equal to the number of
leaves. (A full node is a node that has two children.)
2. (5 points)
Design a linear time algorithm to test whether a binary tree is a binary search tree. Provide
pseudocode for your algorithm and justify that your algorithm is linear in the number of
nodes.
3. (5 points)
Analyze the worst case and best case running times of inserting n elements into an initially
empty binary search tree. For each case, provide details of your analysis starting from counting
relevant operations to an accurate asymptotic characterization.
Part II
Write a parser that parses an arithmetic expression given in infix notation into a binary expression tree. Your parser should support infix expressions consisting of binary operators {‘+’, ‘-’,
‘*’, ‘/’ }, numbers (in integer format), as well as parentheses (which may be nested). Once
an expression has been parsed into an expression tree, your program will additionally be able to
perform preorder and postorder traversals on the tree, and evaluate the expression.
You can perform the parsing either using a stack (worth 15 points) or via recursive descent
(worth 15 points + 5 bonus) using an expression grammar for infix expressions. Both strategies
will be discussed in class and tutorials.
Stack-based Parsing (15 points)
Please review Section 4.2.2 in Weiss which presents a stack-based algorithm for parsing parenthesesfree expressions given in postfix notation. Note that you will first need to apply Dijkstra’s shunting
yard algorithm to convert the given infix expression to postfix.
• You may use the Stack class from the Java Collections Framework.
• Implementation of Dijkstra’s shunting yard algorithm and the subsequent stack-based parsing
algorithm must be your own. You are also required to use the provided ExpressionTree and
ExpressionTreeNode classes (see below).
• Your implementation should check for errors and throw an exception if there are any syntax
problems in the input expression.
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CPSC 331: Spring 2018 HW3
Recursive Descent (15 + 5 points)
An expression grammar for infix expressions is given below.
E –> T { ( “+” | “-” ) T }
T –> F { ( “*” | “/” ) F }
F –> num | “(” E “)”
This grammar generates expressions consisting of the binary operators +, -, * and / as well as
parenthetical expressions.
Notation: In the above grammar, braces {} are used to indicate productions that may repeat 0 or
more times, | separate alternatives, while parentheses () are used for grouping. The only terminal
symbol is a num. For this assignment, you can assume that num ∈ Z.
Note that * and / have higher precedence compared to + and -. Operators with the same
precedence are associated left-to-right (left-associativity), e.g. the expression “2 – 3 + 4” yields
the following tree.
+
– 4
2 3
Before proceeding with your implementation, please make sure you understand the rules of the
grammar and know how to apply them for parsing via recursive descent.
Implementation
Write a Java class called ExpressionTree that parses expressions either using a stack or by
recursive descent. In either case, your class should have the following public methods.
public class ExpressionTree {
private ExpTreeNode root = null ;
// Builds empty tree
public ExpressionTree () {
}
// Parse an expression from a string
public void parse ( String line ) throws ParseException {
}
// Evaluate an expression
public int evaluate () {
return 0;
}
// Return a postfix version of the expression
public String postfix () {
return “”;
}
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CPSC 331: Spring 2018 HW3
// Return a prefix version of the expression
public String prefix () {
return “”;
}
}
A skeleton of this class as well as the class ExpTreeNode are available on D2L.
Additional Requirements
Include as many private methods as necessary to parse a given expression. You can assume that
properly formatted input expressions will have tokens separated by whitespace. However, you
should check for expressions that have syntax issues. If an input expression contains a syntax error,
the parse method should throw a ParseException. In the thrown exception, include a description
of the nature of the error as well as the location of the error in the input string.
When converting expressions to prefix or postfix, please separate tokens using whitespace. Prefix
and postfix expressions should be parentheses free.
Documentation and Testing
For all private methods that you add, please provide Javadoc comments to explain what the methods
are doing.
Write a program to test your parser. Test with both small size expressions as well as expressions with mixed operators, nested parentheses etc. A test program that is compatible with your
implementation will be made available closer to the due date.
Submission
Part I
Please prepare a PDF file called part1.pdf (scanned or typeset) that is packaged with the rest
of the files for Part II. If you are scanning your solution, please submit the scanned pages as a single
PDF file.
Part II
Please package your Java class files in a compressed archive called hw3.zip. Please remove any
driver programs (main methods) that you used to test your implementations. Please make sure
that your name appears at the beginning of each file. If you need to cite any other sources that you
used, please include them either at the beginning of the file ExpressionTree.java or in a separate
file called README.
Please do not place the files in different folders. Your archive should only contain the following
Java files: ExpTreeNode.java, ExpressionTree.java. In addition, your archive should also contain
the file please part1.pdf and optionally a README file if applicable.
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