private:

unordered_map<int, int> nums;

public:

//O(1) add

void add(int number) {

nums[number]++;

}

//O(n) find

bool find(int value) {

int one, two;

for(auto it = nums.begin(); it != nums.end(); it++){

one = it->first;

two = value - one;

if ( (one == two && it->second > 1) ||

(one != two && nums.find(two) != nums.end() ) ){

return true;

}

}

return false;

}