60 solved GATE CS questions on Programming & Data Structures, drawn from 4 exam years and grouped by year. Every question shows the official answer and a step-by-step solution.
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Simulate the code on small inputs before reasoning about general behavior. These selected foundations connect C-language constructs, pointers, recursion, and fundamental data structures. Each structure has insertion, deletion, and search costs that depend on its invariants.
Our study notes and original examples support the PYQs below; they are not official exam questions or a replacement for the current syllabus.
A pointer holds an address. Dereferencing accesses the value at that address. Pointer arithmetic on an array of type T advances by sizeof(T) bytes per unit. A null pointer dereference is undefined behavior. Pass-by-pointer lets a function modify the caller's variable.
Check yourself: What does the pointer point to after the assignment, and is it still valid?
Each recursive call creates a new stack frame with its own local variables. Identify the base case, the recursive reduction, and what each call returns. The total number of frames determines stack depth. Tail recursion reuses frames only when the compiler optimizes it.
Check yourself: Does every recursive path eventually reach the base case?
A singly linked list supports O(1) insertion at the head but O(n) search. A stack is last-in-first-out; a queue is first-in-first-out. Both can be implemented with arrays or linked nodes. Array-based versions may need resizing; linked versions use extra pointer storage.
Check yourself: Are you updating both the pointer and the node it references?
In a binary search tree, left descendants have smaller keys and right descendants have larger keys. Search, insert, and delete are O(h) where h is the height. A balanced BST maintains h = O(log n); an unbalanced one can degrade to O(n). Inorder traversal of a BST yields sorted order.
Check yourself: Does the BST property hold at every node after your operation?
A hash table maps keys to slots via a hash function. Collisions are unavoidable when the key space exceeds the table size. Chaining uses linked lists per slot; open addressing probes for the next available slot. Average-case O(1) lookup depends on a good hash function and a reasonable load factor.
Check yourself: What happens when two different keys hash to the same slot?
Original teaching example · not a PYQ
Original mini-example: trace the output of this C-like function call foo(3), where foo(n) prints n, then if n > 1 calls foo(n−1), then prints n again.
Output: 3 2 1 1 2 3.
Insert keys 5, 3, 7, 2, 4 in order into an initially empty binary search tree (no rebalancing). What is the inorder traversal?
2 3 4 5 7.
5 becomes the root. 3 goes left of 5, 7 goes right. 2 goes left of 3, 4 goes right of 3. Inorder (left-root-right) visits nodes in sorted order: 2, 3, 4, 5, 7.
Supplemental reading, not an official GATE reading list or an endorsement of these notes.
Free supplemental lecture notes and problem sets covering data structures including BSTs, hash tables, and heaps alongside algorithm analysis.
This page shows 60 recent questions from the released archive, newest first. For older questions and complete papers, browse all GATE CS papers. Questions can carry more than one subject tag; counts are not marks weightage.
G(V, E) is said to be 2-colorable if there exists a function such that for every…MSQ · +2 marks · Mediumfoo(n) returns 5 is ______.…NAT · +2 marks · Hardfork() system call is always…NAT · +2 marks · MediumsomeAlgo that takes an undirected graph as input. someAlgo(G) 1. Let be any vertex in . Run BFS on starting…NAT · +2 marks · MediumSLLdel be a function that deletes a node in a singly-linked list given a pointer to the node and a pointer to the head of the list. Similarly, let…MCQ · +1 marks · EasyContinue learning with Success Tracker
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