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

Solution

public class TwoSum {

    Map<Integer, Integer> map = new HashMap<>();

    // Add the number to an internal data structure.
    public void add(int number) {
        map.merge(number, 1, (a, b) -> a + b);
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {
        for (Integer key : map.keySet()) {
            int target = value - key;
            if (target != key && map.containsKey(target)) return true;
            if (target == key && map.get(target) >= 2) return true;
        }
        return false;
    }
}


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