There are some stacks of dishes on the left side of the sink. There aren't any on the right side. A larger dish can never go on top of a smaller dish (this is valid for all stacks on both left and right sides of the sink).
The only thing you may do is take a dish from the top of one stack on the left side, wash it, and place it anywhere on the right side of the sink (given that it doesn't violate the rule above).
What strategy should you use such that once all the dishes are washed, the right side has the least amount of stacks possible?
Specifics: To simplify the problem, all dishes have distinct sizes.
You start with two stacks: 4,1 and 3,2
A possible minimum solution is washing dishes in this order: 2,1,4,3
You end up with two stacks: 2,1 and 4,3