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) -> truefind(7) -> false

class TwoSum {private:    map
     
       fmap;public:    void add(int x)    {        if(!fmap.count(x))fmap[x]=1;        else fmap[x]++;    }    bool find(int target)    {        for (map
      
       ::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;    }};