Use dictionary to store the numbers and their count. For each key, check if the target value - key is also present in dictionary.

```
class TwoSum:
def __init__(self):
"""
Initialize your data structure here.
"""
self.dict = dict()
def add(self, number):
"""
Add the number to an internal data structure..
:type number: int
:rtype: void
"""
if self.dict.__contains__(number) == True:
self.dict[number] += 1
else:
self.dict[number] = 1
def find(self, value):
"""
Find if there exists any pair of numbers which sum is equal to the value.
:type value: int
:rtype: bool
"""
for key in self.dict.keys():
num = value - key
if self.dict.__contains__(num) == True:
if num == key and self.dict[key] > 1:
return True
if key != num:
return True
return False
```