There are 5 cars to be displayed in 5 parking spaces with all the cars
facing the same direction. Of the 5 cars, 3 cars red, 1 is blue, and 1 is
yellow. If the cars are identical except for color （意思是相同颜色的车不能
放一块?), how many different display arrangements of the 5 cars all
possible?
key :20 | 
