<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) {
        unordered_map<int, vector<int>> nMap;
        sort(nums.begin(), nums.end());
        
        int j = 0;
        
        for (int i = 0; i < nums.size(); i++) {

            // Push first on to map
            if (i == 0) {
                nMap[j].push_back(nums[i]);
                continue;
            }

            if (nums[i] == nums[i-1]) {
                continue;
            }

            // Check if current num is +1 more than previous
            if (nums[i] == nums[i - 1] + 1) {
                nMap[j].push_back(nums[i]);
                continue;
            }

            // New key 
            j++;
            // Push new value on to new key
            nMap[j].push_back(nums[i]);
        }
        int result = 0;

        for (const auto& pair : nMap ) {
            if (pair.second.size() > result) {
                result = pair.second.size();
            }
        }

        return result;
    }
};
61209