170two_sumIII.cpp

class TwoSum {
    //use a unordered hashmap to store the numbers.
    unordered_multiset<int> nums;

public:

    // Add the number to an internal data structure.
	void add(int number) {
	    nums.insert(number);
	}

    // Find if there exists any pair of numbers which sum is equal to the value.
	bool find(int value) {
	    for(int i:nums){
	        int counts = ((i == value-i)? 1 : 0);
	        if(nums.count(value-i)>counts){
	            return true;
	        }
	    }
	    return false;
	}
};


// Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum;
// twoSum.add(number);
// twoSum.find(value);