In Classical music, a melodic minor scale has the 6th and 7th notes sharpened when ascending and returned to natural when descending. However, in Jazz and other more modern styles, the melodic minor descends the same way it ascends. An easy way to think of the ascending melodic minor is as a major scale with a flattened third degree.
This table shows the notes of the melodic minor scale in all twelve keys. Remember that the descending melodic minor is the same as the natural minor. To work out the notes for the harmonic minor, simply flatten the 6th degree of the ascending melodic minor.