LeetCode-Two Sum III - Data structure design

public class TwoSum {
    HashMap<Integer,Integer> numCounts = new HashMap<Integer,Integer>();
    List<Integer> nums = new ArrayList<Integer>();

    // Add the number to an internal data structure.
    public void add(int number) {
        if (numCounts.containsKey(number)){
            numCounts.put(number,numCounts.get(number)+1);
        } else {
            nums.add(number);
            numCounts.put(number,1);
        }
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {
        for (int num : nums){
            int otherNum = value - num;
            boolean validPair = (otherNum==num) ? (numCounts.get(num)>=2) : numCounts.containsKey(otherNum);
            if (validPair){
                return true;
            }
        }
        return false;
    }
}


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