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Objectives
Assignment 09: Applications of Stacks
COSC 2336: Data Structures and Algorithms Fall 2020
• More practice with recursion.
• Practice writing some template functions.
• Use stack ADT to implement given algorithms.
• Practice using Stack class container given as a library in a separate file. • Look at some common applications of stacks.
Description
In this assignment, you will be using the Stack abstract data type we developed for this unit and discussed in our lectures, to implement 4 functions that use a stack data type to accomplish their algorithms. The functions range from relatively simple, straight forward use of a stack, to a bit more complex. But in all 4 cases, you should only need to use the abstract stack interface functions push(), pop(), top(), and isEmpty() in order to successfully use our Stack type for this assignment and the function you are asked to write.
NOTE You are to use the Stack ADT abstraction give to you for this assignment. If you are familiar with STL stack containers, you are not to use them for this assignment. Part of the assignment is to look over and learn the Stack ADT implementation we give you here based on our textbook Stack examples.
Setup
For this assignment you will be given the following files:
File Name
assg09-tests.cpp assg09-stackfun.hpp assg09-stackfun.cpp Stack.hpp
Stack.cpp
Description
Unit tests for the member functions
you are to write.
Header file where function prototypes for the functions you write using stacks should go. Implementaiton file, the implementation of the 4 functions you write for this assignment go here. Header file defining a Stack ADT for use in implementing the functions for this assignment. You will not make any modifications in this file, you are only going to be using the given Stack. Implementation file for the Stack ADT
template class. You also do not make any changes in this file either.
Set up a multi-file project to compile the .cpp source files and run them as shown for the class. The Makefile you were given should be usable to create a build project using the Atom editor as required in this class. You will only be adding code to the assg09-stackfun.[hpp|cpp] file in this assignment. The Stack.[hpp|cpp] file contains a Stack container. You are to use this Stack ADT for the 4 functions you are to write for this assignment.
1
The general approach you should take for this assignment, and all assignment is:
Tasks
You should set up your project/code as described in the previous section. In this section we give some more details on implementing the member functions for this assignment. You should perform the following tasks for this assignment:
1. In the first task, we will write a function that will check if a string of parenthesis is matching. Strings will be given to the function of the format “(()((())))”, using only opening “(” and closing “)”. Your function should be named doParenthesisMatch(). It takes a single string as input, and it returns a boolean result of true if the parenthesis match, and false otherwise.
The algorithm to check for matching parenthesis using a stack is fairly simple. A pseudo-code description might be
for each charcter c in expression
do
if c is an open paren '('
push it on stack
if c is a close paren ')':
then
if stack is empty
answer is false, because we can't match the current ')'
else
pop stack, because we just matched an open '(' with a close ')'
endif done
Your function will be given a C++ string class as input. It is relatively simple to parse each character of a C++ string. Here is an example for loop to do this:
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s = “(())”;
for (size_t index = 0; index < s.length(); index++) {
char c = s[index];
// handle char c of the string expression s here
}
2. In the next task, we will also write a function that decodes a string expression. Given a sequence consisting of ‘I’ and ‘D’ characters, where ‘I’ denotes increasing and ‘D’ denotes decreasing, decode the given sequence to
construct a “minimum number” without repeated digits.
An example of some inputs and outputs will make it clear what is meant by a “minimal number”.
sequence IIII -> DDDD -> ID -> IDIDII -> IIDDIDID ->
output
12345
54321
132
1325467
125437698
If you are given 4 characters in the input sequence, the result will be a number with 5 characters, and further only the digits ‘12345’ would be in the “minimal number” output. Each ‘I’ and ‘D’ in the input denotes that the next digit in the output should go up (increase) or go down (decrease) respectively. As you can see for the input sequence “IDI” you have to accommodate the sequence, thus the output goes from 1 to 3 for the initial increase, because in order to then decrease, and also only use the digits ‘123’, we need 3 for the second digit so the third can decrease to 2.
Take a moment to think how you might write an algorithm to solve this problem? It may be difficult to think of any solution involving a simple iterative loop (though a recursive function is not too difficult).
However, the algorithm is relatively simple if we use a stack. Here is the pseudo-code:
for each index, character c in input sequence
do
push character index+1 onto stack (given 0 based index in C)
if we have processed all characters or c == ‘I’ (an increase) then
pop each index from stack and append it to the end of result
endif
done
Your function should be named decodeIDSequence(). It will take a string of input sequence, like “IDI” as input, and it will return a string type, the resulting minimal number. Notice we will be constructing a string to return here, so simply start with an empty string string result = “” and append the digits to the end when you pop them from the stack as described.
3. In the third task, you will write two functions that will be able to sort a stack. First of all, you should write a simpler method that, given an already sorted stack as input, and an item of the same type as the stack type, the item should be inserted into the correct position on the sorted stack to keep it sorted. For example, the stacks will be sorted in ascending order, where the item at the bottom of the stack is the smallest value, and the item at the top is the largest, like this:
top: 8 7 5 3 1 :bottom
If we call the function to insert a 4 into this sorted stack, the result should be:
top: 8 7 5 4 3 1
Your function should be called insertItemOnSortedStack(). This function takes an item as its first parameter, and a reference to a Stack as its second parameter. You should create and use another temporary stack in your function in order to accomplish the task. The pseudo-code to accomplish this insertion is relatively simple:
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given inputStack
and create temporaryStack for this algorithm
while top of inputStack > item we want to insert
do
pop topItem from inputStack
push topItem onto the temporaryStack
done
at this point, items on inputStack are <= to the item we want to insert so push item onto inputStack
now put items back from temporaryStack to original inputStack
while temporaryStack is not empty
do
pop topItem from temporaryStack
push topItem onto the inputStack
done
The tests given for the insert function use an AStack<int> (a stack of integers) for the tests. You can originally create your function to use a Stack<int> & as its second input parameter. It is important that the stack be a reference parameter here. Also notice that instead of specifying an AStack<int> &, we specify the abstract base class Stack<int> &. This is to demonstrate the power of using virtual classes and class abstractions. If you specify the base class, you can pass an AStack or an LStack or any class that is derived from the base Stack class, as long as that class implements all of the virtual functions of the abstract Stack interface. Once you have your function working for Stack<int> &, templatize your function. We practiced creating function templates in a previous assignment. Here it should be relatively simple, you simply need to add the
template <class T>
before the function, and change the <int> to <T> to templatize. Once you do this, you function should still
work and pass the tests using an <int> type.
4. Once you have your insertItemOnSortedStack() template function working, it is even easier to use this function to create a sortStack() function. We could implement this function again using a temporary stack, but for this fourth and final function I want you instead to create a recursive function. A recursive function in this case is going to work in essentially the same way, but we will be using the OS/system function call stack implicitly to perform the algorithm, rather than explicitly creating and using our own temporary stack.
Create a function called sortStack(). This function should take a Stack<string> & (a reference to a Stack of <string> types) as its only parameters. You will later templatize this function as well, but all of the tests of sortStack() use stacks of strings, so get it working first for strings, then try and templatize the function. This is a void function, it doesn’t return a result, but it implicitly causes the stack it is given to become sorted.
The function, as the name implies, will take an unsorted stack, and will sort them in the same order we used previously, e.g. in ascending order with the smallest item at the bottom of the stack, and the largest at the top. The pseudo-code to accomplish this using a recursive algorithm is as follows:
given inputStack as an input parameter
# the base case
if inputStack is empty, do nothing (return)
# the general case
take top item from inputStack and save it in a local variable
call sortStack(inputStack) recursively on this now smaller stack
# on return, the stack should be sorted, so
insertItemOnSortedStack(my item I popped, inputStack)
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Once you have it working for type stacks, also templatize your sortStack() function, so that it will actually work to sort a Stack of any type.
Example Output
Here is the correct output you should get from your program if you correctly implement all the class functions and successfully pass all of the unit tests given for this assignment. If you invoke your function with no command line arguments, only failing tests are usually shown by default. In the second example, we use the -s command line option to have the unit test framework show both successful and failing tests, and thus we get reports of all of the successfully passing tests as well on the output.
$ ./test =============================================================================== All tests passed (47 assertions in 4 test cases)
$ ./test -s
——————————————————————————-
test is a Catch v2.7.2 host application. Run with -? for options
——————————————————————————-
<doParenthesisMatch()> test doParenthesismatch function ——————————————————————————- assg09-tests.cpp:28 …………………………………………………………………….
assg09-tests.cpp:33: PASSED: CHECK( doParenthesisMatch(“”) )
with expansion:
true
… output snipped …
=============================================================================== All tests passed (47 assertions in 4 test cases)
Assignment Submission
A MyLeoOnline submission folder has been created for this assignment. There is a target named submit that will create a tared and gziped file named assg02.tar.gz. You should do a make submit when finished and upload your resulting gzip file to the MyLeoOnline Submission folder for this assignment.
$ make submit
tar cvfz assg09.tar.gz assg09-tests.cpp assg09-main.cpp
assg09-stackfun.hpp assg09-stackfun.cpp Stack.hpp Stack.cpp assg09-tests.cpp
assg09-main.cpp
assg09-stackfun.hpp
assg09-stackfun.cpp Stack.hpp
Stack.cpp
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Requirements and Grading Rubrics
Program Execution, Output and Functional Requirements
Program Style
Your programs must conform to the style and formatting guidelines given for this class. The following is a list of the guidelines that are required for the assignment to be submitted this week.
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