The complete selection process consists of four distinct stages designed to evaluate academic fundamentals, practical engineering skills, and team fit: Round 1: Foundational MCQ Assessment A 1-hour test containing 16 multiple-choice questions testing core concepts across Physics, Computer Science, and Mathematics.

Round 2: Hackathon Part A (Practical Coding) A hands-on technical challenge requiring direct implementation of complex data structures, specifically building a lock-based (locking) tree structure.

Round 3: Elimination Screening A critical filter stage to evaluate your technical foundation, review your approach from the previous rounds, and select candidates for the final evaluation.

Round 4: Final Combined Round A two-part concluding evaluation combining Hackathon Part B (an advanced coding extension of the project) with a Behavioural Interview to evaluate communication, collaboration, and problem-solving mindset.

Explain your approach to solving the part_a problem and then how you can make this multi-threaded part_b.