[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.

Algorithm:

1. unordered_set is needed to be the hashtable.

2. for each one check the whole consecutive sequence containing it. and on each check delete the checked ones.

My Code:

int longestConsecutive(vector<int> num) {
        // use unordered_set to insert and find for constant.
        unordered_set<int> numset;
        for(int i = 0; i < num.size(); ++i)
            numset.insert(num[i]);
        int len = 1;
        for(int i = 0; i < num.size(); ++i){
            int u = num[i];
            int v = u;
            int count = 1;
            if(numset.find(v)!=numset.end()){
                numset.erase(v);
                while(numset.find(--v)!=numset.end()){
                    numset.erase(v);
                    ++count;
                }
                v = u;
                while(numset.find(++v)!=numset.end()){
                    numset.erase(v);
                    ++count;
                }
                if(count < len){
                    len = count;
                }
            }
            
        }
        return len;
    }