Leetcode Two Sum III

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

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解题思路：

关键点在于对重复数字的处理，用hashmap存储值，然后判断value-num == num的情况下，count是否>=2.

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Java code:

public class TwoSum {
    private Map<Integer, Integer> map = new HashMap<Integer, Integer>();
    // Add the number to an internal data structure.
    public void add(int number) {
        if(map.containsKey(number)){
            map.put(number, map.get(number)+1);
        }else {
            map.put(number, 1);
        }
    }

    // Find if there exists any pair of numbers which sum is equal to the value.
    public boolean find(int value) {
        for(Integer i: map.keySet()) {
            int x = value - i;
            if(map.containsKey(x)){
                if(x == i && map.get(i) >= 2){
                    return true;
                }else if( x != i){
                    return true;
                } 
            }
        }
        return false;
    }
}

// Your TwoSum object will be instantiated and called as such:
// TwoSum twoSum = new TwoSum();
// twoSum.add(number);
// twoSum.find(value);

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Reference:

1. http://www.cnblogs.com/EdwardLiu/p/4252598.html