Longest Consecutive Sequence in O(n) with a hash set.

Finding the longest run of consecutive integers without sorting divides candidates who reach for O(n log n) from those who spot the hash-set trick. The signal is one loop invariant that eliminates redundant work. Here is the answer.

Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.