Sufficiency and Maximum Likelihood.

Let be a random sample from the density function given by,

0 otherwise, for known r.

Find a sufficient statistic and maximum likelihood for . Argue that the maximum likelihood estimator is also sufficient for

By the factorization theorem

or any multiple of it is suff for

we get that from the likelihood function.

Then what's the maximum likelihood for theta? Is it possible to illustrate a few steps to kick start? Thank you!