Puzzle 1: Cross river problem

Puzzle 1: 3 Devils and 3 men, cross the river. More Devils will eat man. How to cross, anyone can drive the boat.
Show Solution

Solution:
MMM DDD ---
-> MMM D --- DD
-> MMM DD --- D
-> MMM --- DDD
-> MMM D --- DD
-> M D --- MM DD
-> MM DD --- M D
-> DD --- MMM D
-> DDD --- MMM
-> D --- MMM DD
-> DD --- MMM D
-> --- MMM DDD