[LintCode] Problem 607 - Two Sum III - Data structure design

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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.

Example

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add(1); add(3); add(5);
find(4) // return true
find(7) // return false

Code

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

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

public boolean find(int value) {
    for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
        int val = value - entry.getKey();

        if (map.containsKey(val)) {
            if (val * 2 != value)
                return true;
            else if (val * 2 == value && map.get(val) > 1)
                return true;
        }
    }

    return false;
}