Longest Consecutive Sequence problem LeetCode

 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.


 


Example 1:


Input: nums = [100,4,200,1,3,2]

Output: 4

Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

Example 2:


Input: nums = [0,3,7,2,5,8,4,6,0,1]

Output: 9

Example 3:


Input: nums = [1,0,1,2]

Output: 3

 


Constraints:


0 <= nums.length <= 105

-109 <= nums[i] <= 109



Solution :


class Solution {
    public int longestConsecutive(int[] nums) {
       
       if (nums.length == 0) return 0;

        Arrays.sort(nums); // Sort the array

        int longest = 1;  // Stores the maximum length of the sequence
        int currentStreak = 1;  

        for (int i = 1; i < nums.length; i++) {
            if (nums[i] == nums[i - 1]) {
                continue; // Skip duplicates
            }
            if (nums[i] == nums[i - 1] + 1) {
                currentStreak++; // Extend the sequence
            } else {
                longest = Math.max(longest, currentStreak);
                currentStreak = 1; // Reset streak
            }
        }

        return Math.max(longest, currentStreak);
    }
}

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