Practice Question (Gate 1994)

Duration: 3 min

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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 features a lecture on data structures, specifically focusing on a GATE 1994 problem about stack permutations. The problem asks which of the given output sequences can be generated from the input sequence 1, 2, 3, 4, 5 using a single stack. The instructor systematically evaluates four options: (a) 3, 4, 5, 1, 2; (b) 3, 4, 5, 2, 1; (c) 1, 5, 2, 3, 4; and (d) 5, 4, 3, 1, 2. He uses a visual representation of a stack to trace the necessary push and pop operations for each case, demonstrating the Last In First Out (LIFO) property.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor starts by reading the question and drawing a stack diagram. He analyzes option (a) 3, 4, 5, 1, 2. To output 3, he pushes 1, 2, 3 and pops 3. To output 4, he pushes 4 and pops 4. To output 5, he pushes 5 and pops 5. At this point, the stack contains 1 and 2, with 2 at the top. Since the next required output is 1, but 2 is blocking it, he marks option (a) as incorrect. He then analyzes option (b) 3, 4, 5, 2, 1. He performs the same pushes for 3, 4, and 5. After popping 5, the stack has 1 and 2. He pops 2, then pops 1, successfully matching the sequence. He marks option (b) as correct. He briefly checks option (c) 1, 5, 2, 3, 4, showing that after popping 5, the stack has 2, 3, 4, making it impossible to pop 2 next.

  2. 2:00 – 2:35 02:00-02:35

    The instructor concludes the analysis by checking option (d) 5, 4, 3, 1, 2. He pushes 1 through 5, pops 5, 4, 3. The stack now contains 1 and 2. The next required output is 1, but 2 is on top. He crosses out option (d). He confirms that option (b) is the only valid permutation. He reiterates the core concept that a stack follows the Last In First Out (LIFO) principle, meaning elements must be popped in reverse order of their insertion if they are waiting in the stack.

The lecture effectively demonstrates how to validate stack permutations by simulating the push and pop operations. The key takeaway is that for any valid stack permutation, if an element is pushed onto the stack, it must be popped before any elements pushed after it can be popped. This LIFO constraint is the primary filter used to eliminate invalid options like (a), (c), and (d), leaving (b) as the correct answer.

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