Computer Science Exam #2 Overview

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Questions and Answers

What was the initial perception of the author regarding STEM courses?

They felt discouraged from taking STEM courses. (correct)

They had previous experience in STEM subjects.

They believed they were well-suited for STEM.

They considered STEM courses to be easy.

What motivated the author to persist in the challenging CS class?

The coursework was simplified during the semester.

The effective delivery of content by the professor. (correct)

Consistent practice with classmates was encouraged.

Access to study materials that were easy to understand.

What realization did the author come to during their experience in the CS course?

STEM subjects are not important for career success.

The label of being a 'humanities kid' is limiting. (correct)

Learning programming is only for those with a technical background.

They would never be successful in STEM courses.

How has the author's experience in the CS class influenced their future career path?

They are now more open to challenges and new opportunities. Signup and view all the answers

What was the author's method for comprehending difficult content in class?

Watching lectures multiple times. Signup and view all the answers

What is the primary focus of Exam #2?

Material covered from the beginning of class through the lecture before Exam #2 Signup and view all the answers

Which concept is included in the Exam #2 learning objectives?

Dynamic memory allocation Signup and view all the answers

What type of question format will not be provided during Exam #2?

Syntax reference sheet Signup and view all the answers

What does LIFO stand for in relation to stacks?

Last In First Out Signup and view all the answers

In a call stack for recursive functions, how is the order of execution determined?

By the order of function calls Signup and view all the answers

What additional reading is optional for students in preparation for the course?

Lafore, Chapter 4 Signup and view all the answers

Which of the following is NOT a common operation performed on a stack?

Sort Signup and view all the answers

Which of the following topics is emphasized for understanding in relation to recursion?

Quicksort algorithm Signup and view all the answers

What is the structure of the exam as mentioned in the content?

A mix of short answer, code tracing, and coding tasks Signup and view all the answers

What is the purpose of the 'push' operation in a stack?

To add an item onto the stack Signup and view all the answers

When experiencing a closing structure in the context of matching parentheses, what is the first condition it must satisfy?

It must match the last unmatched opening structure Signup and view all the answers

What deadline is associated with Project #4?

Monday, 10/14, at 9pm Signup and view all the answers

What kind of list structures will be discussed in relation to Exam #2?

Tail pointers and circular linked lists Signup and view all the answers

How are stacks typically represented in programming?

As LIFO data structures Signup and view all the answers

Which of the following describes what happens when an item is popped from a stack?

The item is removed from the top of the stack Signup and view all the answers

What describes the call stack based on the example presented?

It follows a strict order of addition and removal Signup and view all the answers

What is the purpose of the `stk.push(ch)` command in the given code?

To add an opening symbol to the stack Signup and view all the answers

What will happen if the `stk.isEmpty()` condition evaluates to true when processing a closing symbol?

The balanced flag will be set to false Signup and view all the answers

Which of the following symbols is not processed as an opening symbol in the code?

] Signup and view all the answers

What does the function `verify(stk.top(), ch)` likely check?

If the top symbol matches the closing symbol Signup and view all the answers

What will be printed if the stack is not empty but the `balanced` variable is true after the loop?

File does not have balanced symbols Signup and view all the answers

In terms of stack operations, what is the significance of calling `stk.pop()`?

To remove the top matched symbol from the stack Signup and view all the answers

What is the effect of encountering characters other than symbols during the while loop?

They are ignored completely Signup and view all the answers

What structure is used to maintain the symbols while checking for balance?

Stack Signup and view all the answers

What happens when an unmatched closing symbol is encountered while processing the input?

A balanced flag is set to false. Signup and view all the answers

What does the `verify` function check for?

If the top symbol matches the closing symbol correctly. Signup and view all the answers

What output is displayed if the file has balanced symbols?

File has balanced symbols. Signup and view all the answers

How does the program determine if the stack is empty?

By calling the <code>isEmpty</code> method on the stack. Signup and view all the answers

What is the primary data structure used to check for balanced symbols?

CharStack Signup and view all the answers

What will happen if there are unmatched opening symbols left in the stack after processing the input?

The program will indicate the file has unbalanced symbols. Signup and view all the answers

Which of the following symbols would cause the push operation in the stack?

Opening curly brace Signup and view all the answers

What character indicates that an unmatched symbol is detected?

All of the above. Signup and view all the answers

What type of loop is used to read characters from the input stream?

While loop Signup and view all the answers

In what scenario is the variable `balanced` set to false?

When an unmatched closing symbol is found. Signup and view all the answers

Which of the following is NOT an opening symbol in the provided code?

) Signup and view all the answers

What action is performed when a matching closing symbol is found?

Pop the symbol from the stack. Signup and view all the answers

What logic is used to pair opening and closing symbols?

Each symbol has a specific corresponding symbol. Signup and view all the answers

What would happen if `verify` function returned false?

The balanced variable becomes false. Signup and view all the answers

Study Notes

Announcements

Project #4 due on Monday, October 14th at 9 pm.
Reading: zyBooks, Chapter 5.
ZY-4 due on Sunday, October 6th at 11:59 pm.
ZY-5 due on Sunday, October 20th at 11:59 pm.
Optional Auxiliary Reading: Lafore, Chapter 4.
Exam #2 is on Wednesday, October 9th in class.
Exam #2 covers material from the start of the semester through today's lecture, excluding the lecture on Monday, October 7th.
Final exam is on Tuesday, December 10th, 2024, from 7-10 pm. Schedule the exam for 6:00-10:30 pm.

Exam #2 Overview

Exam will be 50 minutes long.
Focus will be on material since the first exam (lectures 10-19) covering topics from Chapter 3-4 in zyBooks and the introduction to Chapter 5.
Topics include:
- Big-O analysis.
- Dynamic memory allocation, arrays vs. linked lists.
- General linked list items: linking nodes, dot notation, traversing a list, inserting/deleting nodes, sorted vs. unsorted lists, edge conditions while processing lists.
- Special list structures: tail pointers, circular linked lists, doubly linked lists.
- The TweetMgr class of projects 1-3, the BigNum class of lectures.
- Recursion: understanding/tracing/writing recursive methods, comparing recursion vs. iteration, divide-n-conquer, Quicksort (recommended to begin work on project #4).
- Basics of stacks.

Exam #2 Format

Short answer questions: multiple choice, fill-in-the-blank, true/false.
Code tracing questions: Identify print statements, errors, workload.
Code writing questions: fill-in-the-blank coding, small methods, short code segments (function headers).
No reference sheets will be provided.

Stacks

Stacks are lists where data is added and removed from a specific end known as the top.
Last In First Out (LIFO) data structure, similar to a stack of cafeteria trays.
Common in computer science: used by compilers to maintain function execution, undo commands in editors, backtracking in mazes or card games.
Stack Abstract Data Type (ADT) operations:
- Create a new empty stack.
- Push (add) an item onto the stack.
- Pop (remove) an item off the stack.
- Retrieve the top item without popping it off.
- Test if the stack is empty.
- Retrieve the size of the stack.
- (Optional) Display the entire stack for debugging.

Brainstormed Stacks Application - Parenthesis Matching

Objective: Write a Java program to verify properly nested and matched parentheses, braces, and brackets.
Requirements:
- Each closing structure (e.g., ), }, ]) must match the last unmatched opening structure (e.g., (, {, [).
- At the end of the file, all opening structures must have a corresponding matching closing structure.

Overview

The code snippet checks if a file has balanced symbols using a stack data structure.
The code checks if the opening symbol of a pair is present in the stack for each closing symbol encountered during file reading.
If the stack is empty while encountering a closing symbol, the code sets the "balanced" variable to false.

Code Functionality

The code reads characters from the file "example.txt" using a FileReader object.
The "while" loop iterates as long as no unpaired closing symbol is detected, and the file reading does not encounter the end of file.
Inside the loop, the code classifies each character as an opening symbol, a closing symbol, or anything else.
For opening symbols, the code pushes them onto the stack.
For closing symbols, the code checks if the stack is empty; if it is, the code sets "balanced" to false to indicate an imbalance.
If the stack is not empty, the code calls the "verify" function to check if the top element on the stack is the opening symbol corresponding to the current closing symbol.
If "verify" returns true, the closing symbol is matched, and the opening symbol is popped from the stack, otherwise, "balanced" is set to false.
After iterating through all the characters, the code checks if "balanced" is true and the stack is empty. If both conditions are satisfied, the output indicates balanced symbols, otherwise, an imbalance is declared.

The verify() function

This function checks if the given opening character and closing character form a valid symbol pair.
It returns true if they form a pair (e.g. '(' and ')'), otherwise it returns false, indicating an imbalance.

Stack Implementation

The code uses an instance of the "CharStack" class to store the opening characters.
The "CharStack" class is not shown in the provided code snippet.

Example Input

The text includes an example of the input string: "{a}[( b)]".

Unbalanced Case

The text mentions "What if this is our input?" indicating a potential unbalanced case.
The example input is not balanced, since it ends with ']' and '(', implying a missing closing symbol for '('.

Potential Error

The example input points to a likely error in the current code.
The code ends the loop at the end of the file, without checking for any remaining symbols in the stack. This could lead to incorrect results.

Important Notes

The "inputStream.read()" method returns -1 when the end of the file is reached.
The code assumes that the input file contains only opening and closing symbols.

Next Steps

The code needs improvement to handle the potential imbalance case with unpaired opening symbols in the stack after reaching the end of the file.
The code lacks error handling for invalid input characters.
The "CharStack" class implementation is missing in the provided code snippet.

Code Walkthrough

The code verifies if parentheses, curly braces, and square brackets in a file are balanced.
The code iterates through each character in the input stream (inputStream) using a while loop.
If the character is an opening symbol ('(', '{', or '['), it is pushed onto a stack (stk).
If the character is a closing symbol (')', '}', or ']'), the code checks if the stack is empty and sets balanced to false if it is.
If the stack is not empty, the code checks if the top element of the stack matches the current closing symbol using the verify function.
If the symbols are matched, the top element is popped from the stack.
The code ignores all other characters that are not opening or closing symbols.
The code checks if the balanced flag is true and the stack is empty to determine if the symbols are balanced.

Test Input Generation

Test Case 1: The file example.txt contains an unclosed opening symbol (e.g., '{').
Test Case 2: The file contains a closing symbol without a corresponding opening symbol (e.g., ')').
Test Case 3: The file contains a closing symbol followed by a closing symbol without a corresponding opening symbol (e.g., '}').
Test Case 4: The file contains mismatched symbols (e.g., '{' followed by ']').

Stack Implementation Options

Array: A stack can be implemented using an array, with the top of the stack at the end of the array.
Linked List: A stack can also be implemented using a linked list, with the top of the stack pointing to the head of the list.
Other Data Structures: A stack can be implemented using other data structures, such as a binary tree or a heap, though these implementations are less common.

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Description

Prepare for the Computer Science Exam #2 with this overview focusing on material from lectures 10-19, specifically Chapters 3-5 in zyBooks. Key topics include Big-O analysis, dynamic memory allocation, and linked lists. Make sure to review your notes and readings to excel in this 50-minute exam.