I want to run code on my device and with an input file. Please write the main() function in C++

Here is the question:

https://leetcode.com/problems/two-sum/

I want to write the

function for this question with a similar function call which is a class member. I also want the input from a text file in the same directory. Since is used in the solution template (I want the same). So please specify, how will I input both vector and target without knowing input size?