The sections of the National Housing Act, as amended, referred to in the plaintiffs' petition, 50 U.S.C.A.Appendix, § 1895, provide, subsection (a), among other things, that any person who demands, accepts, receives or retains any payment of rent in excess of the maximum rents fixed under the Act, shall be liable to the person so paying the same for reasonable attorneys' fees and costs as determined by the court" * * * plus liquidated damages in the amounts of (1) $50, or (2) not more than three times the amount by which the payment or payments demanded, accepted, received or retained exceed the maximum rent which could lawfully be demanded, accepted, received, or retained, as the court in its discretion may determine, whichever in either case may be the greater amount: Provided, That the amount of such liquidated damages shall be the amount of the overcharge or overcharges if the defendant proves that the violation was neither willful nor the result of failure to take practicable precautions against the occurrence of the violation"; and provide further, subsection (c), that "Suit to recover liquidated damages as provided in this section may be brought * * * within one year after the date of violation".