Two Sum solved in Python using brute force and hash map https://leetcode.com/problems/two-sum/

twoSum.py

class Solution:
    def twoSum1(self, nums: List[int], target: int) -> List[int]:
        # O(n^2)
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if target - nums[i] == nums[j]:
                    return [i, j]
        
        return None

    def twoSum(self, nums: List[int], target: int) -> List[int]:
        # O(n)
        hash = {}

        for i in range(len(nums)):
            current = nums[i]
            remainder = target - current
            if remainder in hash:
                return [hash[remainder], i]
            else:
                hash[current] = i
        
        return None