<p>Given an unsorted array of integers <code>nums</code>, return <em>the length of the longest consecutive elements sequence.</em></p>

<p>You must write an algorithm that runs in&nbsp;<code>O(n)</code>&nbsp;time.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [100,4,200,1,3,2]
<strong>Output:</strong> 4
<strong>Explanation:</strong> The longest consecutive elements sequence is <code>[1, 2, 3, 4]</code>. Therefore its length is 4.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,3,7,2,5,8,4,6,0,1]
<strong>Output:</strong> 9
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
</ul>

class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        if not nums: 
            return 0 
        numbers = set(nums)
        seen = set() 
        max_gap = 1
        for num in numbers: 
            if num in seen:
                continue 
            high = low = num 
            seen.add(num)
            while high + 1 in numbers or low - 1 in numbers: 
                if high + 1 in numbers: 
                    high += 1 
                    seen.add(high)
                if low - 1 in numbers: 
                    low -= 1 
                    seen.add(low)
                
                max_gap = max(max_gap, high - low + 1 )
        return max_gap 
        
36790