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Questions and Answers
What was the initial perception of the author regarding STEM courses?
What motivated the author to persist in the challenging CS class?
What realization did the author come to during their experience in the CS course?
How has the author's experience in the CS class influenced their future career path?
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What was the author's method for comprehending difficult content in class?
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What is the primary focus of Exam #2?
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Which concept is included in the Exam #2 learning objectives?
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What type of question format will not be provided during Exam #2?
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What does LIFO stand for in relation to stacks?
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In a call stack for recursive functions, how is the order of execution determined?
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What additional reading is optional for students in preparation for the course?
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Which of the following is NOT a common operation performed on a stack?
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Which of the following topics is emphasized for understanding in relation to recursion?
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What is the structure of the exam as mentioned in the content?
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What is the purpose of the 'push' operation in a stack?
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When experiencing a closing structure in the context of matching parentheses, what is the first condition it must satisfy?
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What deadline is associated with Project #4?
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What kind of list structures will be discussed in relation to Exam #2?
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How are stacks typically represented in programming?
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Which of the following describes what happens when an item is popped from a stack?
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What describes the call stack based on the example presented?
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What is the purpose of the stk.push(ch)
command in the given code?
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What will happen if the stk.isEmpty()
condition evaluates to true when processing a closing symbol?
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Which of the following symbols is not processed as an opening symbol in the code?
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What does the function verify(stk.top(), ch)
likely check?
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What will be printed if the stack is not empty but the balanced
variable is true after the loop?
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In terms of stack operations, what is the significance of calling stk.pop()
?
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What is the effect of encountering characters other than symbols during the while loop?
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What structure is used to maintain the symbols while checking for balance?
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What happens when an unmatched closing symbol is encountered while processing the input?
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What does the verify
function check for?
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What output is displayed if the file has balanced symbols?
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How does the program determine if the stack is empty?
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What is the primary data structure used to check for balanced symbols?
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What will happen if there are unmatched opening symbols left in the stack after processing the input?
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Which of the following symbols would cause the push operation in the stack?
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What character indicates that an unmatched symbol is detected?
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What type of loop is used to read characters from the input stream?
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In what scenario is the variable balanced
set to false?
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Which of the following is NOT an opening symbol in the provided code?
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What action is performed when a matching closing symbol is found?
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What logic is used to pair opening and closing symbols?
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What would happen if verify
function returned false?
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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 awhile
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
tofalse
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.