Analysis: In the process of determining the three digits consisting of 0, 1, 2 and 3, we should determine them one by one. So each problem can be seen as being completed in three steps. (1) required to form three unequal numbers. So the number can be reused, and one hundred can't be taken as 0, so there are three different ways to take it. In ten digits, you can choose any one of the four numbers, and there are four different ways to take it; There are four different ways to take the unit. According to the principle of multiplication, * * * can form 3×4×4=48 unequal three digits. (2) there are no duplicate numbers in the required three digits, and 0 cannot be taken in the hundred digits, so there are three different ways to take it. On the tenth digit, there are three ways to take one digit from 1, 2 and 3, leaving only 0 and the other two digits; In the unit, because the hundreds and tens each take a number, they can only take it from the remaining two numbers. There are two ways. According to the principle of multiplication, * * * has three digits of 3×3×2= 18, and there is no repetition. Solution: Using the principle of multiplication, 3×4×4=48 different three digits can be formed. ② * * * can form 3×3×2= 18 (pieces), and there are no duplicate numbers.