Stack Practice questions

Duration: 7 min

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Inside: a video lesson and guided study material.

Module outline

  1. About Course: About the Course
  2. CS | 01 | Digital Logic and Circuits and Discrete Mathematical Structures: Digital Systems & Boolean Basics, Number System, Number Representation, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Permutation and Combination
  3. CS | 02 | Computer Organization and Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Multiprocessors
  4. CS | 03 | Data Structures and Algorithm: Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Complexity Theory, Advanced Algorithms
  5. CS | 04 | Problem Solving through C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
  6. CS | 05 | Object Oriented Techniques: Object Oriented Technology, Java
  7. CS | 06 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Windows OS, Unix OS
  8. CS | 07 | Database Management Systems: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, Database Security & Authorization, Query Processing & Optimization, File Organization & Indexing
  9. CS | 08 | Computer Networks: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics
  10. CS | 09 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  11. CS | 10 | Internet Technology, Web Design and Web Technology: Internet Fundamentals, Web Design & Development, Protocols & Services, Web Publishing & Hosting, Server Side & Security, Emerging Technologies, JavaScript-Basics, HTML Basics
  12. CS | 11 | System Analysis And Design: Fundamentals of Systems and Information Systems, SDLC and Development Approaches, Software Documentation and Software Requirements Specification (SRS), SDD and Quality Assurance, Security, Risk Management & Maintenance
  13. CS | 12 | Information Security and Cyber Laws: Cyber Threats and Malware Attacks, Role of Internet and Web Services, Security in Mobile and Wireless Computing, Electronic Data Interchange and E-Commerce, Physical Security and Cryptography Basics, Intrusion Detection Systems (IDS), Cyber Safety and Security
  14. CS | 13 | Computer Graphics: Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing
  15. GS Paper | 01 | Indian and World Geography: Geography
  16. GS Paper | 02 | History: History
  17. GS Paper | 03 | Indian Economy & Social Development: Indian Economy
  18. GS Paper | 04 | General Science: Biology, Chemistry, Physics
  19. GS Paper | 05 | Elementary Maths: Number System, Divisibility Rules, HCF LCM, Percentage, Profit and Loss, Simple Interest and Compound Interest, Ratio and Proportion (Ratios), Average, Time and Work, Speed Time and Distance, Algebra, Mensuration and Geometry, Data Interpretation, Arithmetic, Statistics, Probability, Sequence and Series (Series), Mixture and Alligation, Calculus, Trigonometry, Vectors, Factors, Multiples, Divisibility, HCF & LCM, Mensuration — Perimeter, Area, Surface Area, Volume, Data Handling, Graphs & Probability, Coordinates & Graphs, Higher Mathematics — Trigonometry, Quadratics, Polynomials, Progressions, Statistics, Logarithms, समतल क्षेत्रमिति / Plane Mensuration
  20. GS Paper | 06 | Indian Polity and Governance: Polity
  21. GS Paper | 07 | Current Events: GK- Current Affairs
  22. UPLT Live Classes Notes: UPLT Live Classes
  23. UPLT Full Mock Tests Tier 1:
  24. UPLT Full Mock Tests Tier 2:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The video presents a computer science problem asking to identify the functionality of a specific C function named `fun`. The instructor systematically analyzes the code by tracing its execution with a concrete example, `n = 81`. He explains the recursive logic where the function divides the input by 3 repeatedly. The core concept is determining whether a number is a power of 3 based on its divisibility properties. The instructor contrasts a valid case (81) with an invalid case (21) to verify the function's behavior against the provided multiple-choice options. The lesson emphasizes understanding base cases and recursive steps in algorithm analysis.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The session begins with the instructor writing `n = 81` on the whiteboard to serve as a test input. He notes that 81 is a multiple of 3 ($3 imes 27$). He starts the trace for `fun(81)`. The first condition `if (n == 0 || n == 1)` evaluates to false. The second condition `if (n % 3 != 0)` is also false because 81 is perfectly divisible by 3. Consequently, the code executes `return fun(n/3)`, which translates to a recursive call `fun(27)`. He writes `fun(81) -> fun(27)` on the board to visualize the call stack. He highlights that the function keeps dividing by 3 as long as the remainder is zero.

  2. 2:00 – 5:00 02:00-05:00

    The instructor continues the trace for `fun(27)`. He writes `27 % 3 = 0` and `27/3 = 9`, leading to `fun(9)`. The process repeats: `fun(9)` calls `fun(3)`, and `fun(3)` calls `fun(1)`. Upon reaching `n = 1`, the base case `if (n == 0 || n == 1)` becomes true, and the function returns `1`. To ensure this isn't a coincidence, he tests `n = 21`. `21 % 3 = 0` leads to `fun(7)`. Since `7 % 3` is not 0, the function returns `0`. This confirms the function returns 1 for powers of 3 and 0 otherwise. He writes `21/3 = 7` and `7 % 3 = 1` to show the failure point where the condition `if (n % 3 != 0)` becomes true.

  3. 5:00 – 7:20 05:00-07:20

    The instructor summarizes the findings by drawing a visual chain: $81 ightarrow 27 ightarrow 9 ightarrow 3 ightarrow 1$. He explicitly writes $3^4 = 81$ to reinforce that 81 is a power of 3. He reviews the options: (A) claims it returns 1 for multiples of 3, which is incorrect because 21 is a multiple but returns 0. (C) and (D) are also incorrect based on the return values. He selects option (B): "It returns 1 when n is a power of 3, otherwise returns 0". He crosses out the incorrect options to finalize the answer. He emphasizes that the function essentially checks if the number can be reduced to 1 by repeated division by 3, which is the definition of a power of 3.

The lecture provides a clear methodology for debugging recursive functions. By manually stepping through the recursion stack with specific inputs, the instructor deduces the mathematical property the code implements. The distinction between "multiple of 3" and "power of 3" is the key takeaway, demonstrated through the contrasting traces of 81 and 21. The visual aids, such as the call chain and the modulo calculations, are crucial for understanding the flow. The final conclusion solidifies the relationship between the code logic and the mathematical concept of powers.

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