Explain Quick Sort. What is its worst-case complexity? How do you avoid it?

Difficulty: 6/10

partitioning, pivot selection, worst-case O(n^2)

Quick Sort

Quick Sort selects a pivot, partitions the array around the pivot, and recursively sorts the resulting partitions. Its average expected complexity is O(n log n), but poor pivot choices can create highly unbalanced partitions and lead to O(n²) worst-case time. Randomized pivot selection or robust pivot strategies greatly reduce the probability of consistently bad partitions.

javascript

1
Average/expected time: O(n log n).
2
Worst case: O(n²).
3
Randomized pivoting reduces adversarial pivot behavior.
4
Median-of-three can improve practical pivot quality.
5
Typical in-place implementations use O(log n) expected recursion stack.

Scenario Questions

0-2 years experience

2-5 years experience

1Our service sorts incoming batches of up to 10,000 records using quick sort, but we see occasional spikes in latency. How would you investigate and mitigate the worst‑case scenario?

Follow-up Questions