Quote:I see a lot of codes in the Internet that solve this problem with arrays or using a bit array that indicate whether we use a number or not. The issue is that in this question, we are not allowed to use -any- type of array or other data structures like vector ,etc.
Since any variable is also a bit array, there is not solution while respecting all constraint.
Quote:I don't know how to do this without any arrays.
Start by solving with arrays, it will give you a starting point to think on how to get rid of arrays and what to make recursive. At least you will have a working solution.
We do not do your HomeWork.
HomeWork is not set to test your skills at begging other people to do your work, it is set to make you think and to help your teacher to check your understanding of the courses you have taken and also the problems you have at applying them.
Any failure of you will help your teacher spot your weaknesses and set remedial actions.
Any failure of you will help you to learn what works and what don't, it is called 'trial and error' learning.
So, give it a try, reread your lessons and start working. If you are stuck on a specific problem, show your code and explain this exact problem, we might help.