170. 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.

For example,

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

解法1：

要注意一些细节。需要排除找到的数字不是自己，所以要统计每一个数字出现的次数。
C++

1

Java

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public class TwoSum {
    /** Initialize your data structure here. */
    HashMap<Integer, Integer> map = null;
    public TwoSum() {
        map = new HashMap<Integer, Integer>();
    }
    /** Add the number to an internal data structure.. */
    public void add(int number) {
        map.put(number, map.getOrDefault(number, 0) + 1);
    }
    /** Find if there exists any pair of numbers which sum is equal to the value. */
    public boolean find(int value) {
        for (int key : map.keySet()) {
            int target = value - key;
            if (target == key && map.get(key) > 1 ) {
                return true;
            } else if (target != key && map.containsKey(target)) {
                return true;   
            }
        }
        return false;
    }
}
/**
 * Your TwoSum object will be instantiated and called as such:
 * TwoSum obj = new TwoSum();
 * obj.add(number);
 * boolean param_2 = obj.find(value);
 */