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. Paper-2 | Programming & Data Structures: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  3. Paper-2 | Databases / DBMS & SQL: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control
  4. Paper-2 | Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos
  5. Paper-2 | Computer Networks & Security: 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, Network Access Technologies, Network Security
  6. Paper-2 | Digital Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Floating Point Rep
  7. Paper-2 | Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management
  8. Paper-2 | Theory of Computation: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines
  9. Paper-2 | Computer Organization & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Programming the Basic Computer
  10. Paper-2 | Compiler Design: Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment
  11. Paper-1 | General Awareness: Polity, Physics, Biology, Chemistry, Static General Knowledge, GK- Current Affairs, History, Geography, Indian Economy, Environment
  12. Paper-1 | Logical Reasoning: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Data Interpretation, Blood Relations, Syllogisms, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Selection Decision Table (Decision Making), Clock, Calendar, Cubes & Dices, Directions (Direction Test), Analogy, Seating Arrangements, Analytical Reasoning (Counting Figures Reasoning)
  13. Paper-1 | Quantitative Aptitude: Ratio and Proportion (Ratios), Mixture and Alligation, Permutation and Combination, Number System, HCF LCM, Speed Time and Distance, Average, Age Problems, Percentage, Profit and Loss, Time and Work, Pipe and Cistern, Simple Interest and Compound Interest, Powers and Exponents (Surds and Indices), Mensuration and Geometry, Probability, Statistics, Arithmetic, Algebra
  14. Paper-1 | English: Vocabulary, Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Construction, Cloze Test (Cloze Passage)
  15. Coal India Previous Year Paper:
  16. Engineering Mathematics: Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Linear Algebra, Calculus
  17. Coal India Mock Test:
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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