UGC NET Computer Science 2025 Previous Year Questions (PYQs) – Page 1 of 9

• Digital Signature → Confirms authenticity and integrity 
• Hash Function → Produces a fixed-size digest 
• AES → Symmetric encryption algorithm 
• RSA → Asymmetric encryption algorithm

• LL(0) is the weakest (no lookahead, top-down).
• LR(0) is stronger than LL(0) (bottom-up, no lookahead).
• SLR(1) adds 1-symbol lookahead using FOLLOW sets → accepts more grammars than LR(0).
• LALR(1) merges LR(1) states; more powerful than SLR(1) but below LR(1).
• LR(1) is the most powerful among these deterministic bottom-up parsers.

• An adjacency matrix represents a graph using a 2D array (matrix).
• This type of storage uses sequential memory allocation — rows and columns are stored in contiguous memory.
• Hence, this method is called a Sequential Representation of a graph.

• User-Mode Programs have the lowest priority and are preemptible.
• Kernel System Service Routines run in kernel mode and can be preempted by higher priority tasks like interrupts.
• Bottom Half Interrupt Handlers execute after the top half and have higher priority than kernel threads.
• Top Half Interrupt Handlers handle immediate hardware responses and have the highest priority.

Goal: Find a set of attributes whose closure covers all attributes of R = {A, B, C, D, E}.

Check (1) CD⁺:
From C → F we get F. D gives nothing further. So CD⁺ = {C, D, F}.
Missing A, B, E ⇒ not a key.

Check (2) EC⁺:
Start {E, C}. Using E → A ⇒ add A. Using A → B ⇒ add B. Using EC → D ⇒ add D.
Therefore EC⁺ = {E, C, A, B, D} = {A, B, C, D, E}. Covers all attributes of R ⇒ key.

Check (3) AE⁺:
A → B gives B; E → A adds nothing new. No way to reach C or D ⇒ not a key.

Check (4) AC⁺:
A → B gives B; C → F gives F. No E or D ⇒ not a key.

Answer: (2) EC

Note: F is outside R, so while C → F is valid, a key must cover only attributes of R. EC⁺ covers {A, B, C, D, E}.

Answer: 4) B and C only

• Binary Search Tree (BST): Not necessarily balanced; height can degrade to O(n).
• AVL Tree: Height-balanced by definition (balance factor −1, 0, +1); height is O(log n).
• Red-Black Tree: Enforces black-height properties that keep height O(log n); treated as a height-balanced binary tree.
• B-Tree: Balanced (all leaves at the same level) but not a binary tree; the term “height-balanced tree” typically refers to binary trees. Hence excluded here.

Translate each statement:
(a) “If intelligent then unhappy” ⇒ P → ¬Q.
(b) “Neither intelligent nor happy” ⇒ ¬P ∧ ¬Q.
(c) “Being not intelligent is necessary for being happy” ⇒ Q → ¬P.
(d) “Not intelligent implies unhappy” ⇒ ¬P → ¬Q.

Only Option 3 matches all four translations.

Answer: 3

Answer: (4) C, B, D, A

Explanation:
The standard steps for designing a dynamic programming algorithm are:

1. (C) Characterize the structure of an optimal solution.
2. (B) Recursively define the value of an optimal solution.
3. (D) Compute the value of an optimal solution (usually bottom-up).
4. (A) Construct the optimal solution from the computed information.

Hence, the correct order is C → B → D → A.