LeetCode Longest Consecutive Sequence

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        int len = num.size();
        
        int max_cons = 0;
        int cur_cons = 0;
        
        unordered_map<int, int> sgn;
        unordered_map<int, int>::iterator iter;
        for (int i=0; i<len; i++) {
            sgn.insert(make_pair(num[i], 0x1));
        }
        
        for (int i=0; i<len; i++) {
            iter = sgn.find(num[i]);
            if (iter == sgn.end()) continue; // illegal case, should not hit
            if (iter->second == 0) continue; // this range has been scaned
            iter->second = 0;
            cur_cons = 1;
            
            int try_n = num[i];
            // search towards negative
            while (try_n != INT_MIN) {
                try_n--;
                iter = sgn.find(try_n);
                if (iter == sgn.end()) break;
                iter->second = 0;
                cur_cons++;
            }
            try_n = num[i];
            // search towards positive
            while (try_n != INT_MAX) {
                try_n++;
                iter = sgn.find(try_n);
                if (iter == sgn.end()) break;
                iter->second = 0;
                cur_cons++;
            }
            if (cur_cons > max_cons) max_cons = cur_cons;
        }
        
        return max_cons;
    }
};