Two Sum III - Data structure design

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

• Time: O(n)
• Space: O(1)

public class TwoSumIII {

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

    public void add(int i) {
        map.put(i, map.containsKey(i) ? map.get(i) + 1 : 1);
    }

    public boolean find(int target) {
        for (Integer i : map.keySet()) {
            if (map.containsKey(target - i)) {
                if (i == target - i && map.get(i) < 2) {
                    continue;
                }
                return true;
            }
        }
        return false;
    }
}