Coding - Memory Allocator

In an OpenAI interview, the Memory Allocator problem is a classic low-level systems question. It tasks you with implementing a simulated dynamic memory manager that supports allocate and free operations, similar to malloc and free in C. PracHub +1 3 0)

The Problem Statement

You must design a system that manages a contiguous block of memory of size Ncap N𝑁 (usually provided at initialization). The allocator must track which bytes are in use and which are free, efficiently handling interleaved requests for memory. PracHub +2 3 8 0)

Core Operations

• allocate(size): Find the leftmost contiguous block of at least size free units. Mark this block as "allocated" and return its starting index. If no sufficient contiguous space exists, return -1.
• free(id) or free(ptr): 3 5 6 7 0) Release the memory associated with a specific ID or pointer. Crucial Step: You must coalesce (merge) newly freed blocks with adjacent free blocks to reduce fragmentation. PracHub +4

Key Interview Challenges

OpenAI's version typically moves beyond a "naive" solution to test your production-engineering judgment: PracHub +1 3 4

• Efficiency: Aim for 𝑂(log𝑁) or better performance per operation rather than 𝑂(𝑁) brute-force scans.
• Fragmentation: You are expected to discuss and handle both internal fragmentation (wasted space within a block) and external fragmentation (gaps between blocks).
• Data Structures: Be prepared to justify your choice of structures, such as Segregated Free Lists, Interval Trees, or a Buddy System.
• Edge Cases: Handle "double-free" errors, invalid pointers, and zero-size requests. www.jointaro.com +3

Example Scenario

If you initialize memory with size 10: 0)

1. allocate(3) -> returns index 0 (Block 0–2 occupied).
2. allocate(4) -> returns index 3 (Block 3–6 occupied).
3. free(index 0) -> Block 0–2 becomes free.
4. allocate(2) -> returns index 0 (Reuses free block 0–1; 2 is still free).

Would you like to see a Python implementation using an efficient interval-tracking approach, or do you want to dive into the system design trade-offs?

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