Many of your teachers will be content if you can simply remember the most important points that have been covered in the class. Be prepared to do both - remember the material, and solve problems creatively. In many American colleges, you get an exception made to some rule or grading factor if you have a good reason. For instance, if you become very ill and miss an exam, your professor may agree to let you re-take it, or make some other arrangement with you. This is usually up to the teacher to decide.
Administrators also can make exceptions, though there is usually more paperwork involved.
For example, you may be a professional programmer without a degree who is returning to school. Instead of just taking a required introductory programming class, you may file a petition requesting that the class requirement be waived for you, because of the knowledge reflected in your work record. In fact, if you are persistent, you can accomplish a lot through the use of petitions and other appeals. The only limit is your imagination. This can be a valuable tactic for surviving the difficult process of getting a degree in a foreign country in an unfamiliar language.