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);