Question 18 of 513
1Z0-829 Working with Arrays and Collections Practice Question
A developer is working on a high-performance trading application that processes market data. The system needs to maintain a sorted list of order IDs (Long values) that are frequently inserted and removed. The current implementation uses a TreeSet<Long> to store the order IDs. The application is experiencing performance degradation under high load, and profiling shows that the TreeSet operations are the bottleneck. The developer considers replacing the TreeSet with a data structure that offers O(log n) insertion and removal but also supports O(log n) indexed access (e.g., get by index) for batch processing. Which of the following should the developer choose to improve performance while maintaining the sorted order and adding indexed access?
⚠ Common exam trap
It's easy for candidates to assume TreeSet or TreeMap can provide indexed access via toArray() or keySet(), overlooking that those operations are O(n) and defeat the purpose of O(log n) performance requirements.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
No standard Java Collections class fulfills all requirements; consider a custom implementation.
No standard Java Collections class provides O(log n) insertion, removal, and O(log n) indexed access while maintaining sorted order. TreeSet offers O(log n) insertion/removal but lacks indexed access; ArrayList provides O(1) indexed access but requires O(n log n) sorting after each insertion; PriorityQueue offers O(log n) insertion/removal but only O(1) peek access, not indexed access. A custom data structure like an order statistic tree (e.g., a balanced binary search tree with subtree sizes) is needed to meet all requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
No standard Java Collections class fulfills all requirements; consider a custom implementation.
Why this is correct
No built-in collection provides O(log n) insertion, removal, and indexed access simultaneously.
- ✗
Replace with TreeMap<Long, Boolean> and use the key set for iteration and indexed access via keySet().toArray().
Why it's wrong here
TreeMap key set is sorted but indexed access via toArray() is O(n) each time.
- ✗
Replace with PriorityQueue<Long> and use poll() for removal and toArray() for indexed access.
Why it's wrong here
PriorityQueue does not maintain sorted order for iteration and does not support indexed access.
- ✗
Replace with ArrayList<Long> and use Collections.sort() after each insertion.
Why it's wrong here
Sorting after each insertion is O(n log n), worse than TreeSet O(log n).
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Last reviewed: Jun 11, 2026
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