Longest Consecutive Sequence - LeetCode 128
An Interactive Visual Explainer
Idea By: Chetan Pachpande | Executed By: Claude
Longest Consecutive Sequence - LeetCode 128
Problem Description:
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
You must write an algorithm that runs in O(n) time complexity.
Example: Input: nums = [100,4,200,1,3,2] → Output: 4 (sequence: [1,2,3,4])
Algorithm Complexity:
Time Complexity: O(n) - Each element is visited at most twice
Space Complexity: O(n) - HashSet to store all elements
Algorithm Steps:
1. Create HashSet and add all elements from array
2. For each element, check if it's the start of a sequence (num-1 not in set)
3. If start of sequence, count consecutive numbers (num+1, num+2, ...)
4. Update maximum sequence length if current sequence is longer
5. Return the maximum sequence length found