Cant we write code from scratch on CodeStudio?

I was solving the problem called Game of 3 under maths and number theory and it had vector in codestub issue is I dont know stl and have solved the same problem on my local compiler succesfully using arrays. So cant we write it that way instead
https://www.codingninjas.com/codestudio/problems/game-of-3_1868996?leftPanelTab=0