LeetCode #1 - Two Sum

Background: You are given an array of integers and a target integer. Your task is to find two numbers such that they add up to the target. You may assume that each input would have exactly one solution, and you may not use the same element twice. You can return the answer in any order.
Problem Statement: Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice.
Typed Signature: def two_sum(nums: List[int], target: int) -> List[int]:
Example 1:
Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3, 2, 4], target = 6
Output: [1, 2]
Explanation: Because nums[1] + nums[2] == 6, we return [1, 2].
Constraints: 2 <= nums.length <= 10^4, -10^9 <= nums[i] <= 10^9, -10^9 <= target <= 10^9.