<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 {
public:
    int longestConsecutive(vector<int>& nums) {
    int n=nums.size();

    if (n==0){
        return 0;
    }

    if (n==1){
        return 1;
    }

    std::sort(nums.begin(), nums.end());
    vector<int> Nums;
    Nums.push_back(nums[0]);
    for (int i = 1; i < n; ++i) {
        if (nums[i]!=nums[i-1]){
            Nums.push_back(nums[i]);
        }
    }
    

    int m=Nums.size();

    if (m==1){
        return 1;
    }

    int begin=0;
    int Maxlength=INT_MIN;
    for (int last = 1; last < m; ++last) {
        if (Nums[last]!=Nums[last-1]+1){
            begin=last;
        }
        Maxlength= max(Maxlength, last-begin+1);
    }

    return Maxlength;

}
};
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