<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 {
    unordered_map<int, int> parent;
public:
    int findParent(int u){
            if(parent[u] == u) return u;
            return parent[u] = findParent(parent[u]);
        }

    void unionWithNearest(int u){
        int pu = findParent(u);

        int pred = u-1;
        int succ = u+1;
        if(parent.find(pred) != parent.end()){
            parent[pred] = pu;
        }
        if(parent.find(succ) != parent.end()){
            parent[u] = parent[succ];
        }
    }

    int longestConsecutive(vector<int>& nums) {
        for(auto w: nums){
            parent[w] = w;
            unionWithNearest(w);
        }

        int ans = 0;
        for(auto w: nums){
            // cout << w << "- " << par << endl;
            ans = max(findParent(w)-w+1, ans);
        }
        return ans;
    }
};
79400