Brute Force vs O(n): Longest Consecutive Sequence Explained

How do you find the longest consecutive sequence in O(n) without sorting? The key isn't to start counting from every number. Instead, ask one simple question: “Is this the START of a sequence?” In this video, we go from: Brute force — keep searching for num + 1 Sorting — make consecutive numbers neighbors HashSet — check existence in O(1) The key optimization — only start when num - 1 doesn't exist Example: [2, 20, 4, 3, 5] 2 → 3 → 4 → 5 ↓ length = 4 Final complexity: ⚡ O(n) time 💾 O(n) space Don't memorize the code — understand why the code works. This walkthrough is designed for software engineers and students preparing for technical assessments. By focusing on algorithm optimization, you will gain a clearer understanding of how to manage unsorted integers effectively. We review the code logic step-by-step so you can apply these same principles to similar array problems in your own projects. Subscribe for weekly data structure and algorithm breakdowns, and comment below if you want to see the solution for a different array problem next.