[LeetCode] Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

Solution:

class Solution {
public:
    set<int> dataset;
    
    int continousLength(int number)
    {
        int len = 0, l = number, r = number + 1;
        set<int>::iterator itr;
        while((itr = dataset.find(l)) != dataset.end())
        {
            dataset.erase(itr);
            l--;
            len++;
        }
        while((itr = dataset.find(r)) != dataset.end())
        {
            dataset.erase(itr);
            r++;
            len++;
        }
        
        return len;
    }
    
    int longestConsecutive(vector<int> &num) {
        int MaxLen = 0; 
        dataset.clear();
        for(int i = 0 ; i < num.size() ; i++)
           dataset.insert(num[i]);
        
        for(int i = 0;i < num.size();i++)
            MaxLen = max(continousLength(num[i]), MaxLen);
        
        return MaxLen;
    }
};