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.

　　The key point is that for each number say Val in the array, we only need to determine whether its neighbor (Val-1 and Val+1) is in the array and  for a consecutive sequence we only need to know the the boundary and the length information。

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int size = num.size();
        if(size < 2) return size;
        
        map<int, int> myMap;
        for(int i = 0; i< num.size(); i++)
             myMap.insert(pair<int, int>(num[i],1));
        
        int maxLen = 0;
        map<int, int>::iterator m_it;
        map<int, int>::iterator temp_it;
        
        for(m_it = myMap.begin(); m_it != myMap.end();m_it++)
        {
        
            if(m_it->second == 0) continue;
            int len = 1;
            int low = m_it->first;
            int high = low;
            while(true)
            {
              temp_it= myMap.find(low-1);
              if(temp_it == myMap.end())
                break;
              low--;
              len++;
              temp_it->second = 0;
            }
            
            while(true)
            {
                 temp_it=   myMap.find(high+1) ;
                 if(temp_it == myMap.end())
                break;
                high++;
                len++ ;
                temp_it->second = 0;
            }
            
            maxLen = maxLen < len ? len : maxLen ; 
            
            
        }
        
        
        return maxLen ;
        
        
    }
};