Given an array of integers, find two numbers such that they add up to a specific target number. Implement a function `twoSum(nums: List[int], target: int) -> List[int]` that returns the indices of the two numbers. Constraints: 1 <= nums.length <= 10^4, -10^9 <= nums[i] <= 10^9, you may assume that each input would have exactly one solution, and you may not use the same element twice. Examples: Input: nums = [2,7,11,15], target = 9; Output: [0,1]. Input: nums = [3,2,4], target = 6; Output: [1,2].