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

Here is my cpp solution with O(nlog(n)):

vector two_sum(vector &numbers, int target) {
    vector result;
    vector numbers_dup = vector(numbers);

    sort(numbers_dup.begin(), numbers_dup.end());

    int left = 0, right = numbers_dup.size() - 1;
    while(left <= right) {
        int sum = numbers_dup[left] + numbers_dup[right];

        if(sum == target) {
            //find the idex of numbers_dup[left] and numbers_dup[right]
            for(int i = 0; i < numbers.size(); i++) {
                if(numbers[i] == numbers_dup[left] || numbers[i] == numbers_dup[right]) {
                    result.push_back(i);
                }
                if(result.size() == 2) {
                    return result;
                }
            }
        }
        else if(sum > target) {
            right--;
        }
        else {
            left++;
        }
    }
}

Check out my blog for the detailed explanation. https://algorithm.pingzhang.io/Array/two_sum_problem.html