<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:
    vector<int> nums;
    int solve1(){
         sort(nums.begin(), nums.end());
        int n=nums.size();
        if(!n) return 0;

        int ans=0, cnt=0, exp=nums[0];
        for(auto it: nums){
            if(it == exp){
                exp++;
                cnt++;
            } 
            else if(it==exp-1) continue;
            else {
                ans = max(ans, cnt);
                exp=it+1;
                cnt=1;
            }
        }
        return max(ans, cnt);
    }
    int solve2(){
        unordered_set<int> s;
        for(auto it: nums) s.insert(it);
        int cnt=0, ans=0;
        for(auto it: s){
            if(s.find(it-1)==s.end()){
                while(s.find(it)==s.end()){
                    it++;
                    cnt++;
                }
                ans = max(cnt, ans);
            }
        }
        return ans;
    }
    int longestConsecutive(vector<int>& nums) {
        this->nums=nums;
        return solve1();
        // return solve2();
    }
};
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