One potential error is a missing or erroneous implementation of the '?' instruction.

My code is working on all test cases, but it still gives "Exit Code: 1" due to Time Limit Exceeded, while the only operations I am doing are scanning characters and doing corresponding stack, var setting or output operations. How to know what am I doing wrong?

I think you can divide as you want but it is usual to divide in egal parts because it is simpler.

please someone explain what is the interval on? I mean whether we should divide the curve into n equal parts or the interval of x i.e, [a,b] into n equal parts? The answer to my doubt is not apparent from the accompanying diagram. I wonder if the diagram is to scale or not.