[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.

[cpp]
class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        unordered_set<int> hash;

        for(int i = 0; i < num.size(); i++){
            hash.insert(num[i]);
        }

        unordered_set<int>::iterator it;
        int result = 0;
        int tmp_elem;
        int cnt;
        unordered_set<int>::iterator tmp_it;

        while(!hash.empty()){
            cnt = 1;
            it = hash.begin();

            int elem = *it;
            hash.erase(it);

            tmp_elem = elem + 1;
            while((tmp_it = hash.find(tmp_elem)) != hash.end()){
                cnt++;
                tmp_elem++;
                hash.erase(tmp_it);
            }

            tmp_elem = elem - 1;
            while((tmp_it = hash.find(tmp_elem)) != hash.end()){
                cnt++;
                tmp_elem--;
                hash.erase(tmp_it);
            }
            result = max(result, cnt);

        }

        return result;

    }
};

补充：软件开发 , C++ ,