LeetCode 128: Longest Consecutive Sequence in O(n) Time with Python

LeetCode #128 – Longest Consecutive Sequence | Python Implementation I implemented a HashSet-based approach to find the longest consecutive sequence in O(n) time without sorting. The key insight is identifying sequence starts: if a number has no left neighbor (n-1 not in set), it marks the beginning of a potential sequence. From there, we count consecutive elements by checking n+1, n+2, and so on until the sequence breaks. This avoids redundant work by only initiating sequences from their true starting points. This pattern is essential in time-series analysis, event stream processing, and database query optimization for range detection. Key Takeaway: The "sequence start" check is what makes this O(n) instead of O(n²). Each element is visited at most twice: once in the outer loop and once during sequence counting. Recognizing when to skip unnecessary iterations is crucial for optimizing nested-loop patterns. Time: O(n) | Space: O(n) #LeetCode #DataStructures #Python #HashSet #Arrays #CodingInterview #ProblemSolving #SoftwareEngineering

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