# COP4530 Programming Assignment #4 Binary Tree and Its Application solution

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## Educational Objectives:

In this assignment you are to gain experience with
the design and implementation of a binary tree and its application in
converting postfix expressions into infix expressions, as well as practice with
developing recursive algorithms.

Task: Implement a binary expression tree and use the tree to convert postfix
expressions into infix expressions

## Project Requirements:

In this project, you are asked to develop a binary expression tree and use the
tree to convert postfix expressions into infix expressions. In this project, a
postfix expression may contain 4 types of operators: multiplication (*), division
(/), plus (+), and minus (-).

We assume that multiplication and division have
the same precedence, plus and minus have the same precedence, and
multiplication and division have higher precedence than plus and minus. All
operators are left-associative (i.e. associate left-to-right).

## Binary Expression Tree:.

Build a binary expression tree class called “BET”.
Your BET class must have a nested structure named “BinaryNode” to contain
the node-related information (including, e.g., element and pointers to the
children nodes).

In addition, BET must at least support the following interface
functions (you may have more in your implementation but do not change the
test driver):

Public interface
 BET(): default zero-parameter constructor. Builds an empty tree.
 BET(const string& postfix): one-parameter constructor, where
parameter “postfix” is string containing a postfix expression. The tree
should be built based on the postfix expression. Tokens in the postfix
expression are separated by spaces.

 BET(const BET&): copy constructor — makes appropriate deep copy of
the tree
 ~BET(): destructor — cleans up all dynamic space in the tree
COP4530 Data Structures and Algorithm Analysis
 bool buildFromPostfix(const string& postfix): parameter “postfix” is
string containing a postfix expression.

The tree should be built based on
the postfix expression. Tokens in the postfix expression are separated
by spaces. If the tree contains nodes before the function is called, you
need to first delete the existing nodes. Return true if the new tree is built
successfully.

Return false if an error is encountered.
 const BET & operator= (const BET &): assignment operator — makes
appropriate deep copy
 void printInfixExpression(): Print out the infix expression. Should do
this by making use of the private (recursive) version
 void printPostfixExpression(): Print the postfix form of the expression.
Use the private recursive function to help
 size_t size(): Return the number of nodes in the tree (using the private
recursive function)

 size_t leaf_nodes(): Return the number of leaf nodes in the tree. (Use
the private recursive function to help)
 bool empty(): return true if the tree is empty. Return false otherwise.

Private helper functions (all the required private member functions must
be implemented recursively):
 void printInfixExpression(BinaryNode *n): print to the standard
output the corresponding infix expression. Note that you may need to
add parentheses depending on the precedence of operators. You
should not have unnecessary parentheses.

 void makeEmpty(BinaryNode* &t): delete all nodes in the subtree
pointed to by t.
 BinaryNode * clone(BinaryNode *t): clone all nodes in the subtree
pointed to by t. Can be called by functions such as the assignment
operator=.
 void printPostfixExpression(BinaryNode *n): print to the standard
output the corresponding postfix expression.

 size_t size(BinaryNode *t): return the number of nodes in the subtree
pointed to by t.
 size_t leaf_nodes(BinaryNode *t): return the number of leaf nodes in
the subtree pointed to by t.
Make sure to declare as const member functions any for which this is
appropriate
COP4530 Data Structures and Algorithm Analysis

## Conversion to Infix Expression:.

To convert a postfix expression into an
infix expression using a binary expression tree involves two steps. First, build
a binary expression tree from the postfix expression. Second, print the nodes
of the binary expression tree using an in-order traversal of the tree.

The basic operation of building a binary expression tree from a postfix
expression is similar to that of evaluating postfix expression. Refer to Section
4.2.2 for the basic process of building a binary expression tree from a postfix
expression.

Note that during the conversion from postfix to infix expression, parentheses
may need to be added to ensure that the infix expression has the same value
(and the same evaluation order) as the corresponding postfix expression.

expression should also be separated by a space. The following are a few
examples of postfix expressions and the corresponding infix expressions.

postfix expression infix expression
4 50 6 + + 4 + ( 50 + 6 )
4 50 + 6 + 4 + 50 + 6
4 50 + 6 2 * + 4 + 50 + 6 * 2
4 50 6 + + 2 * ( 4 + ( 50 + 6 ) ) * 2
a b + c d e + * * ( a + b ) * ( c * ( d + e ) )

## Other Requirements:

 Analyze the worst-case time complexity of the private member
function makeEmpty(BinaryNode* & t) of the binary expression tree.
Give the complexity in the form of Big-O. Your analysis can be informal;
however, it must be clearly understandable by others. Name the file
containing the complexity analysis as “analysis.txt”.

 You can use any C++/STL containers and algorithms
 If you need to use any containers, you must use the ones provided in
C++/STL. Do not use the ones you developed in the previous
projects.

 Create a makefile that will compile the provided driver program (see
below) with your class, into an executable called “proj4.x”
COP4530 Data Structures and Algorithm Analysis
 Your program MUST check invalid postfix expressions and report
errors. We consider the following types of postfix expressions as invalid
expressions: 1) an operator does not have the corresponding operands,
2) an operand does not have the corresponding operator. Note that an
expression containing only a single operand is a valid expression (for
example, “6”). In all other cases, an operand needs to have an
operator.

The sample driver program (proj4_driver.cpp) is attached to this assignment
and included in Canvas. The driver accepts input from terminal, or the input is
redirected from a file that contains the postfix expressions to be converted.
Each line in the file (or typed by user) represents a postfix expression. We
assume that the tokens in a postfix expression are separated by space.

#### Submitting

Tar up all of your C++ source files and header files that you develop for this
project, as well as the makefile and the analysis.txt file into one tar archive,
and submit online via Canvas,in the “Assignments” section. Use the
Assignment 4 link to submit. Make sure to tar your files correctly.
Your tar file should be named in this format, all lowercase:
lastname_firstname_p4.tar
Example: My tar file would be: Gaitros_david_p4.tar