class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        numlist = set(nums) 
        #you need set or else it's too slow 
        longest = 0 
        
        #the concept is you are checking to see if there is a left neighbor. If not, then there is a new sequence of conseuctive numbers. 
        
        for n in nums: 
            if (n - 1) not in numlist: 
                length = 0 
                while (n + length) in numlist: 
                    length += 1 
                longest = max(length, longest)
        return longest