<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:
        def find(forest, key):
            print(key)
            dset = forest[key]
            if dset[0] == key:
                return key
            return find(forest, dset[0])

        def union(forest, key1, key2):
            pkey1 = find(forest, key1)
            pkey2 = find(forest, key2)

            set1 = forest[pkey1]
            set2 = forest[pkey2]

            if set1[1] > set2[1]:
                head = set1
                child = set2
            else:
                head = set2
                child = set1
            
            head[1] = head[1] + child[1]
            child[0] = head[0]

            return head[0]

        longest = 0
        forest = {}
        # (parent, size)
        for n in nums:
            if n not in forest:
                forest[n] = [n, 1]
                head = n
            else:
                continue
            
            if n + 1 in forest and n - 1 in forest:
                head = union(forest, n + 1, union(forest, n - 1, n))
            elif n + 1 in forest:
                head = union(forest, n + 1, n)
            elif n - 1 in forest:
                head = union(forest, n - 1, n)
            longest = max(longest, forest[head][1])
        
        return longest
40750