looks like someone didn't even read the specs...

Assume that n is always exchangeable with [100, 50, 20] bills

This code can't handle numbers like 231,232,237.....

Since Array would start with 0, I guess to make sure the last item in marked[] will corresponed to the largest num (in abs) in the lst[]? This way if that num itself is a prime number, say 101, this prime factor, i.e. itself, will also be included in the calculation.

Why does the length of the marked array have to be m+1?

If you are interesting about the formula you can check this.

So this is a generalized version of this? https://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B%AF

I assume the (n+1) factor signifies what you're saying is (firstNum + lastNum)

Hint: 1+2+3+...+10 = ( lastOfNum + firstOfNum )* howManyNum /2 = (10+1)*(10-1+1)/2 = 55

Can you explain how your algorithm for expect works?