Two sum III - Data structure design

Time: O(N); Space: O(N); easy

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.

Example 1:

Input: s = {TwoSum} [add(1); add(3); add(5)]

Output: [s.find(4)] True; [s.find(7)] False

[1]:

from collections import defaultdict

class TwoSum(object):
    def __init__(self):
        """
        initialize your data structure here
        """
        self.lookup = defaultdict(int)

    def add(self, number):
        """
        Add the number to an internal data structure.
        :rtype: nothing
        """
        self.lookup[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.lookup:
            num = value - key
            if num in self.lookup and (num != key or self.lookup[key] > 1):
                return True
        return False

[2]:

s = TwoSum()
s.add(1)
s.add(3)
s.add(5)
assert s.find(4) == True
assert s.find(7) == False