This really depends on your goal. If fat-loss muscle gain/looking toned, etc. is your goal, you should be doing a minimum of 3 days a week of strength training. Again depending on the goal, training intensity, etc. a coach can write you a 4 day, 5 day or an everyday training program. If you are starting off with 3 evenly spaced out workouts in a week, full body workouts would be a great way to go.
If you are doing 4 times a week, you can probably switch to an upper body – lower body split or some other split. At the end of the day, there is no black and white rule as to what an ideal program should look like. Your program will depend on your goal, lifestyle, training level and health history.
To answer this question again, if the goal is to build muscle, lose fat, get in shape. In this context, a minimum of 3 times a week strength training is required.