Learning Partitions using Rank Queries

We consider the problem of learning an unknown partition of an n element universe using rank queries. Such queries take as input a subset of the universe and return the number of parts of the partition it intersects. We give a simple O(n)-query, efficient, deterministic algorithm for this problem. We also generalize to give an O(n + klog r)-rank query algorithm for a general partition matroid where k is the number of parts and r is the rank of the matroid.