Longest Consecutive Sequence

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

Constraints:

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109

SOLUTION:

class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        nums = set(nums)
        maxLen = 0
        for num in nums:
            if (num - 1) not in nums:
                l = 1
                while (num + l) in nums:
                    l += 1
                maxLen = max(maxLen, l)
        return maxLen