leetcode[170]Two Sum III - Data structure design

Design and implement a TwoSum class. It should support the following operations: add and find.

add - Add the number to an internal data structure.
find - Find if there exists any pair of numbers which sum is equal to the value.

For example,

add(1); add(3); add(5);
find(4) -> true
find(7) -> false

class TwoSum 
{
private:
    map<int,int> fmap;
public:
    void add(int x)
    {
        if(!fmap.count(x))fmap[x]=1;
        else fmap[x]++;
    }
    bool find(int target)
    {
        for (map<int,int>::iterator iter=fmap.begin();iter!=fmap.end();iter++)
        {
            int i=iter->first;
            if(fmap.count(target-i))
            {
                if(i!=target-i)return true;
                else if(fmap[i]>=2)return true;
            }
        }
        return false;
    }
};