[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;

    }

};