128. Longest Consecutive Sequence

#link to problem https://leetcode.com/problems/longest-consecutive-sequence/description/
class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        nums_set = set(nums)
        head_set = set()
        out = 0
        cur_max = 1
        
        for num in nums:
            if num - 1 not in nums_set:
                head_set.add(num)
        
        head_list = list(head_set)

        for num in head_list:
            cur = num
            while cur + 1 in nums_set:
                cur += 1
                cur_max += 1
            out = max(out, cur_max)
            cur_max = 1
        return out