What part of it you are not able to understand?
why we multiply (y+1) with x*y . and the editorialist comes to the solution y * (y+1) * (f(r) - f(l-1)) of this.
What part of it you are not able to understand?
why we multiply (y+1) with x*y . and the editorialist comes to the solution y * (y+1) * (f(r) - f(l-1)) of this.