LeetCode 128. Longest Consecutive Sequence

Problem Statement

(Source) Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in $O(n)$ complexity.

Solution

class Solution(object):
    def longestConsecutive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        res = 0
        se = set(nums)
        for num in se:
            if num - 1 not in se:
                tmp = 1
                x = num + 1
                while x in se:
                    tmp += 1
                    x += 1
                res = max(res, tmp)
        return res