<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 {}; }
        radixSort(nums);
        int lcs = 1, temp = 1;
        int n = nums.size();

        for (int i = 0; i < n-1; i++){
            if (nums[i] == nums[i+1]){
                continue;
            }

            if (nums[i]+1 == nums[i+1]){
                temp++;
                if (temp > lcs){
                    lcs = temp;
                }
            } else {
                
                temp = 1;
            }
        }
        return lcs;
    }

    void radixSort(vector<int>& nums){
        int minimum = *min_element(nums.begin(), nums.end());
        if (minimum < 0){
            for (int& i: nums){
                i -= minimum;
            }
        }
        int maximum = *max_element(nums.begin(), nums.end());

        for (long int i = 1; maximum / i > 0; i*=10){
            countingSort(nums, i);
        }

        if (minimum < 0){
            for (int& i: nums){
                i += minimum;
            }
        }
    }

    void countingSort(vector<int>&nums, long int exp){
        int count[10] = {0};
        int n = nums.size();
        vector<int> ans(n);
        for (int i = 0; i < n; i++){
            count[(nums[i]/exp) % 10]++;
        }

        for (int i = 1; i < 10; i++){
            count[i] += count[i-1];
        }

        for (int i = n-1; i >=0; i--){
            ans[count[(nums[i]/exp) % 10]-1] = nums[i];
            count[(nums[i]/exp) % 10]--;
        }
        nums = ans;
    }
};
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