<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:
        class Node:
            def __init__(self,val):
                self.val=val
                self.left=None
                self.right=None
        nums=set(nums)
        seenset=set()
        max_size=0
        for i in nums:
            temp_max=1
            if(i in seenset):
                continue
            else:
                x=i
                seenset.add(x)
                while(x-1 in nums):
                    seenset.add(x-1)
                    temp_max+=1
                    x-=1
                x=i
                while(x+1 in nums):
                    seenset.add(x+1)
                    temp_max+=1
                    x+=1
            max_size=max(max_size,temp_max)
        return max_size
37150