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Algorithmic Complexity & Code-Level Optimization Questions

Reasoning about the time and space complexity of code and applying local optimizations that materially change performance. Covers Big-O analysis and performance modeling, data-structure selection, hot-loop and allocation reduction, and knowing when an algorithmic change beats micro-optimization. Emphasizes performance-aware coding grounded in complexity rather than premature tuning.

EasyTechnical
91 practiced
Explain how CPU caches (L1/L2/L3) affect performance when scanning a large array sequentially versus performing random-access lookups (e.g., hashing). Use examples to illustrate expected cache hit/miss behavior and the implications for per-element latency in data processing tasks.
MediumTechnical
105 practiced
Implement a Python function that processes a stream of integers and maintains the top-k largest elements seen so far using O(k) extra memory and O(log k) time per element. Provide code for insertion/update and retrieval of sorted top-k, and explain time and space complexity and how this approach fits a streaming ETL job.
HardSystem Design
107 practiced
You're joining a very wide table (hundreds of columns) with another large table on a key in Hadoop MapReduce. Reducers are OOM-ing. Describe optimization strategies (projection, column pruning, bloom filters, map-side joins, combiners, external sort/merge) and analyze how each reduces memory and I/O costs in terms of asymptotic and practical impacts.
EasyTechnical
87 practiced
You're responsible for a Java-based ETL job that has become noticeably slower. Describe a step-by-step profiling and benchmarking approach to identify where time is spent. Include which tools you'd use (e.g., JFR, jstack, perf), metrics to collect, how to create representative benchmarks, and how to ensure reproducible measurements.
EasyTechnical
88 practiced
Given the table schema:
transactions(transaction_id BIGINT, user_id INT, amount DECIMAL(10,2), occurred_at TIMESTAMP)
Table has 500M rows, average row size 200 bytes, stored in 8 KB pages on a single HDD. Estimate sequential read I/O cost in seconds to perform a full table scan on a node with 200 MB/s sustained disk throughput. Show your assumptions and computation.

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