128. Longest Consecutive Sequence

class Solution(object):
    def longestConsecutive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        nums = set(nums)
        maxlen = 0
        while nums:
            first = last = nums.pop()
            while first - 1 in nums:
                first -= 1
                nums.remove(first)
            while last + 1 in nums:
                last += 1
                nums.remove(last)
            maxlen = max(maxlen, last - first + 1)
        return maxlen