twoSum Algorithm : How to improve this?

Question

I felt like doing an algorithm and found this problem on leetcode

Given an array of integers, find two numbers such that they add up to a specific target num

Answer 1

Swift code with Time Complexity O(n) and Space complexity O(n):

import UIKit

class Solution{
    func twoSum(_ nums: [Int], _ target: Int) -> [Int]{
        var finalArray = [Int]()
        var newDictionary = [Int:Int]()
        for i in 0..