[LeetCode] 170. 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

Two Sum题的拓展，设计一个数据结构，实现添加数字和找目标数字的功能。用HashMap来存数字和查找。

Java:

public class TwoSum {
	private HashMap<Integer, Integer> elements = new HashMap<Integer, Integer>();
 
	public void add(int number) {
		if (elements.containsKey(number)) {
			elements.put(number, elements.get(number) + 1);
		} else {
			elements.put(number, 1);
		}
	}
 
	public boolean find(int value) {
		for (Integer i : elements.keySet()) {
			int target = value - i;
			if (elements.containsKey(target)) {
				if (i == target && elements.get(target) < 2) {
					continue;
				}
				return true;
			}
		}
		return false;
	}
}

 Python:

class TwoSum(object):

    def __init__(self):
        self.dic = {}

    def add(self, number):
        if number not in self.dic:
            self.dic[number] = 1
        else:
            self.dic[number] += 1

    def find(self, value):
        dic = self.dic
        for num in dic:
            if value - num in dic and (value - num != num or dic[num] > 1):
                return True
        return False

　　

Python:

class TwoSum(object):

    def __init__(self):
        self.lookup = defaultdict(int)
        
    def add(self, number):
        self.lookup[number] += 1

    def find(self, value):
        for key in self.lookup:
            num = value - key
            if num in self.lookup and (num != key or self.lookup[key] > 1):
                return True
        return False

C++:

class TwoSum {
public:
    void add(int number) {
        ++m[number];
    }
    bool find(int value) {
        for (auto a : m) {
            int t = value - a.first;
            if ((t != a.first && m.count(t)) || (t == a.first && a.second > 1)) {
                return true;
            }
        }
        return false;
    }
private:
    unordered_map<int, int> m;
};

　　

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