Combinations, Randomness, Sorting

Problems

Problem 23 - Pick elements from a list at random.

Problem 24 - Pick lottery numbers.

Problem 25 - Randomly pick an permutation of elements from a list.

Problem 26 - Generate all combinations of a specified number of elements of a list.

Problem 27 - Generate all disjoint sets of elements of a list.

Problem 28a - Sort a list of lists by their lengths.

Problem 28b - Sort a list of lists by the frequency of their lengths.