Two Sum III - Data structure design LT170

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 

Idea 1. Similar to Two Sum LT1, if numbers are unique, set would be enough, otherwise map to store frequency for each number. 遍历hashmap, 对于每个数num，找target - num,

record[num] >= 2 if target - num = num

record[target - num] >= 1 if target - num != num

Time complexity: O(1) for add, O(n) for find, or alternatively add set to store the sum, so that O(n) for add, O(1) for find

Space complexity: O(n)

public class TwoSum {
    private Map<Integer, Integer> record = new HashMap<>();

    public void add(int number) {
        record.put(number, record.getOrDefault(number, 0) + 1);
    }

    public boolean find(int value) {
        for(int key: record.keySet()) {
            int another = value - key;
            if(key == another) {
                if(record.get(another) >= 2) {
                    return true;
                }
            }
            else {
                if(record.containsKey(another)){
                    return true;
                }
            }
        }
        return false;
    }

    public static void main(String[] args) {
        TwoSum subject = new TwoSum();
        subject.add(1);
        subject.add(3);
        subject.add(4);
        System.out.println(subject.find(4));
        System.out.println(subject.find(7));
    }
}

slightly more conciser:

public class TwoSum {
    private Map<Integer, Integer> record = new HashMap<>();

    public void add(int number) {
        record.put(number, record.getOrDefault(number, 0) + 1);
    }

    public boolean find(int value) {
        for(int key: record.keySet()) {
            int another = value - key;
            if((key == another && record.get(another) >= 2)
               || (key != another && record.containsKey(another))){
                return true;
            }
        }
        return false;
    }
}