<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) {
        if(nums.size()==0){
            return 0;
        }
        else if(nums.size()==1){
            return 1;
        }
        int arr[nums.size()];
        for(int i=0;i<nums.size();i++){
            arr[i]=nums[i];
        }
        int n=sizeof(arr)/sizeof(arr[0]);
        sort(arr,arr+n);
        int a=1;
        int b=0;
         int index = 2;  

         for (int i = 1; i < n; i++) {
         if (arr[i] != arr[index - 1]) {
         arr[index] = arr[i];
         index++;
         }
         }
        for(int i=0;i<n-1;i++){
            if(arr[i]+1==arr[i+1]){
                a+=1;
            }
            else{
                a=1;
            }
            if(b<=a){
                b=a;
            }
        }
        return b;
    }
};
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