Computer Science Engineering Mock Interview Questions & Practice

Explain how you would detect if two strings are anagrams of each other.

Key points to cover:

• Character frequency count comparison
• Sorting approach as an alternative, O(n log n)
• Discusses the time/space trade-off between the two approaches

How would you find the lowest common ancestor of two nodes in a binary search tree?

Key points to cover:

• Uses the BST property while traversing from the root
• States O(h) time complexity
• Contrasts with general binary-tree LCA needing a full traversal

How does quicksort's pivot selection affect its performance?

Key points to cover:

• Poor pivot choice (e.g. first element on sorted input) degrades to O(n^2)
• Randomized or median-of-three pivot selection helps avoid the worst case
• Connects pivot quality to partition balance

Explain the difference between multithreading and multiprocessing.

Key points to cover:

• Multithreading shares memory within one process, lower overhead
• Needs synchronization to avoid shared-state issues
• Multiprocessing uses separate memory spaces, higher isolation and overhead

Compare paging and segmentation as memory management schemes.

Key points to cover:

• Paging uses fixed-size units, transparent to the programmer
• Segmentation uses variable-size logical units (code/data/stack)
• Notes segmentation can suffer external fragmentation

How does a condition variable work, and what problem does it solve?

Key points to cover:

• Lets a thread wait/block until a specific condition becomes true
• Signaled by another thread
• Solves busy-waiting inefficiency compared to polling a flag

What is a subquery, and give an example of when you'd use one.

Key points to cover:

• A query nested inside another query
• Useful for filtering based on an aggregate or related table result
• Gives a concrete example (e.g. rows above a subquery-computed average)

Explain Third Normal Form (3NF) and what problem it solves.

Key points to cover:

• 2NF plus no transitive dependency
• Non-key columns must depend only on the primary key
• Removes redundancy caused by indirect (transitive) dependencies

Explain the difference between the READ COMMITTED and REPEATABLE READ isolation levels.

Key points to cover:

• READ COMMITTED prevents dirty reads
• READ COMMITTED still allows non-repeatable reads within a transaction
• REPEATABLE READ additionally prevents non-repeatable reads

What is the role of the Network layer, and what protocol is most associated with it?

Key points to cover:

• Handles logical addressing
• Handles routing of packets between networks
• Associates it with IP (Internet Protocol)

What is the purpose of TCP's flow control, and how is it achieved?

Key points to cover:

• Prevents a fast sender from overwhelming a slow receiver
• Achieved via a sliding window mechanism
• Receiver advertises how much data it can currently accept

What is the purpose of TLS/SSL in network security?

Key points to cover:

• Provides encryption (confidentiality)
• Provides integrity
• Provides authentication of the server (and optionally client)

What is abstraction, and how does it differ from encapsulation?

Key points to cover:

• Abstraction exposes only essential features/behavior, hiding complexity
• Focuses on WHAT an object does
• Encapsulation is about HOW that hiding is achieved (bundling + access control)

Explain the Strategy pattern and what problem it solves.

Key points to cover:

• Encapsulates interchangeable algorithms/behaviors behind a common interface
• Behaviors can be swapped at runtime
• Solves the problem of many conditional branches selecting between behaviors

Explain the Open/Closed Principle (the 'O' in SOLID).

Key points to cover:

• Software entities should be open for extension but closed for modification
• New behavior should be addable without changing existing, tested code
• Typically achieved via abstraction/polymorphism