Why is the genealogy in Ruth different from Luke?

In Ruth 4:18-22, the genealogy recorded is different from Luke Luke 3:23-38. Now these are the generations of Perez: Perez fathered Hezron, 19 Hezron fathered Ram, Ram fathered Amminadab, 20 Amminadab fathered Nahshon, Nahshon fathered Sa…