Longest Consecutive Sequence is a Medium problem with a beautiful O(n) Hash Set trick — this video explains exactly why checking "n-1 not in set" is the key insight.
What you'll learn:
✅ Why sorting is O(n log n) and Hash Set beats it
✅ The sequence-start condition: only count when n-1 is NOT in the set
✅ Visual walkthrough: [100, 4, 200, 1, 3, 2] → answer: 4 (sequence 1,2,3,4)
✅ Clean Python code with while loop streak counting
✅ Why this problem is a favorite in AI/ML system design rounds
🧠 Practice this problem yourself:
👉 https://codedive.in/longest-consecutive-sequence
🚀 codedive.in — 207 curated DSA problems for AI/ML engineers. O(n) time. O(n) space. No excuses.
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⏱ Timestamps:
0:00 - Problem Statement
0:30 - Why Not Sorting?
1:00 - Hash Set + Start Condition
1:45 - Visual Walkthrough
2:30 - Python Code
3:00 - Complexity Analysis
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