170. Two Sum III - Data structure design

• Difficulty: Easy

• Topics: Hash Table, Design

• Similar Questions:

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Problem:

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 1:

add(1); add(3); add(5);
find(4) -> true
find(7) -> false

Example 2:

add(3); add(1); add(2);
find(3) -> true
find(6) -> false

Solutions:

class TwoSum {
public:
    /** Initialize your data structure here. */
    TwoSum() {

    }

    /** Add the number to an internal data structure.. */
    void add(int number) {
        ++count[number];
    }

    /** Find if there exists any pair of numbers which sum is equal to the value. */
    bool find(int value) {
        for (auto valueCount : count) {
            int target = value - valueCount.first;
            auto it = count.find(target);
            if (it != count.end() && (target != valueCount.first || it->second > 1)) return true;
        }
        return false;
    }
private:
    unordered_map<int, int> count;    
};

/**
 * Your TwoSum object will be instantiated and called as such:
 * TwoSum* obj = new TwoSum();
 * obj->add(number);
 * bool param_2 = obj->find(value);
 */