longest-consecutive-sequence leetcode C++

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.

C++

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        int len = nums.size();
        unordered_set<int> se;
        for(int i=0;i<len;i++)
            se.insert(nums[i]);
        int maxLen = 0;
        for(int i=0;i<len;i++){
            int tmpLen = 1;
            for(int tmp = nums[i] + 1;se.count(tmp);tmpLen++,tmp++)
                se.erase(tmp);
            for(int tmp = nums[i] - 1;se.count(tmp);tmpLen++,tmp--)
                se.erase(tmp);
            maxLen = max(tmpLen, maxLen);
        }
        return maxLen;
    }
};