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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