Java:

Background A set is a collection of elements with no duplicates. From the list [1,4,3,1,2,3,4,1,2), we have the set of numbers (1,4,3,2) - the same list, but with all duplicates removed. A sorted set is a set whose elements are all sorted. From the list (1,4,3,1,2,3,4,1,2), we have the sorted set of numbers (1,2,3,4) -the same list, but with all duplicates removed and all elements sorted. The union between two sets combines the elements from both sets. If we have repeated elements, they are only listed once in the results. For example, the union of (1,2,3,4,5) and (1,3,5,7,9) is (1,2,3,4,5,7,9). The intersection between two sets is all the elements that are common to both sets. For example, the intersection of (1,2,3,4,5) and (1,3,5,7,9) is (1,3,5). (1, 3, and 5 are the only numbers that appear in both sets.)