170. Two Sum III

题目：

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

链接： http://leetcode.com/problems/two-sum-iii-data-structure-design/

 2/20/2017, Java

public class TwoSum {
    HashMap<Integer, Integer> s = new HashMap<Integer, Integer>();
    /** Initialize your data structure here. */
    public TwoSum() {

    }
    
    /** Add the number to an internal data structure.. */
    public void add(int number) {
        if (s.containsKey(number)) {
            s.put(number, s.get(number) + 1);
        } else {
            s.put(number, 1);
        }
    }
    
    /** Find if there exists any pair of numbers which sum is equal to the value. */
    public boolean find(int value) {
        Integer v;
        for(Integer key: s.keySet()) {
            v = value - key;
            if (v != key && s.containsKey(v)) return true;
            if (v == key && s.get(key) > 1) 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);
 */