LeetCode 170. Two Sum III – Data structure design

Description

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

Design a data structure that accepts a stream of integers and checks if it has a pair of integers that sum up to a particular value.

Implement the TwoSum class:

  • TwoSum() Initializes the TwoSum object, with an empty array initially.
  • void add(int number) Adds number to the data structure.
  • boolean find(int value) Returns true if there exists any pair of numbers whose sum is equal to value, otherwise, it returns false.

Example 1:

Input
["TwoSum", "add", "add", "add", "find", "find"]
[[], [1], [3], [5], [4], [7]]
Output

[null, null, null, null, true, false]

Explanation TwoSum twoSum = new TwoSum(); twoSum.add(1); // [] –> [1] twoSum.add(3); // [1] –> [1,3] twoSum.add(5); // [1,3] –> [1,3,5] twoSum.find(4); // 1 + 3 = 4, return true twoSum.find(7); // No two integers sum up to 7, return false

Constraints:

  • -105 <= number <= 105
  • -231 <= value <= 231 - 1
  • At most 5 * 104 calls will be made to add and find.

Explanation

Use a list to track the elements added and a set to track complements.

Python Solution

class TwoSum:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums = []

    def add(self, number: int) -> None:
        """
        Add the number to an internal data structure..
        """
        self.nums.append(number)
        

    def find(self, value: int) -> bool:
        """
        Find if there exists any pair of numbers which sum is equal to the value.
        """
        complements = set()
        for num in self.nums:
            if value - num in complements:
                return True
            
            complements.add(num)
            
        return False
            
            

# Your TwoSum object will be instantiated and called as such:
# obj = TwoSum()
# obj.add(number)
# param_2 = obj.find(value)
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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