Leetcode128.最长连续序列

class Solution(object):
    def longestConsecutive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if nums is None or len(nums) == 0:
            return 0
        num_set = set()
        for num in nums:
            num_set.add(num)
        res = 1
        for num in nums:
            if num not in num_set:
                continue
            else:
                num_set.remove(num)

            forward_count = self.check_forwrad(num, num_set)
            backward_count = self.check_backwrad(num, num_set)
            res = max(res, 1 + forward_count + backward_count)
        return res

    def check_forwrad(self, num, num_set):
        count = 0
        num += 1
        while num in num_set:
            num_set.remove(num)
            count += 1
            num += 1
        return count

    def check_backwrad(self, num, num_set):
        count = 0
        num -= 1
        while num in num_set:
            num_set.remove(num)
            count += 1
            num -= 1
        return count