[LeetCode] 170. Two Sum III - Data structure design

 Problem : https://leetcode.com/problems/two-sum-iii-data-structure-design/

M = Value - N.   Use hash table to find whether M exists when given Value and N.

class TwoSum:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.seen = {}
        self.memo = set()
        
    def add(self, number: int) -> None:
        """
        Add the number to an internal data structure..
        """
        
        if number in self.seen:
            self.seen[number] += 1
        else:
            self.seen[number] = 1
        
    def find(self, value: int) -> bool:
        """
        Find if there exists any pair of numbers which sum is equal to the value.
        """
        
        if value in self.memo: return True

        for n in self.seen.keys():
            if value - n == n:
                if self.seen.get(n, 0) >= 2: 
                    self.memo.add(value)
                    return True
            elif self.seen.get(value - n, 0) > 0: 
                self.memo.add(value)
                return True
        
        return False