You'd be hard pressed to do it in one day.
From Salerno to Vietri sul Mare
Is a 15 min bus ride. There is no ferry dock in Vietri. Do this on a seperate
day. Maybe combine it with Maiori by ferry.
Bus timetable. Amalfi Coast.
https://www.positano.com/en/bus-schedule
Ferry timetable.
https://www.travelmar.it/downloads/orari_travelmar.pdf
To visit Positano, Amalfi and Ravello
might be 1 too many. Check both the bus and ferry schedules to see if you can connect the three. Your best bet might be Ferry Salerno-Amalfi then first bus to Ravello. Return to Amalfi and ferry to Positano then bus back to Salerno.