As one learns programming, how useful it is to spend time to solve hard problems? Like, I saw a problem solving site where one task is for example to find a regular expression for decimal numbers divisible by 9 or do regular expression for a particular problem that is as small as possible (in sen...

I need to determine time complexity of the next code: j1=1 j2=1 for i=1 to n k=j1 while k<=j2 s=s+j k=k+1 j1=j1+2i+1 j2=j2+4i+3 return s So the problem is because I have that j1 and j2 are changing over iterations in while loop, can someone help me? I need to find T(n).