Union and Intersection

Part of the Logic & Flow section of Coddy's Swift journey — lesson 19 of 56.

Sets shine when you ask membership questions involving two collections.

let a: Set = [1, 2, 3, 4]
let b: Set = [3, 4, 5, 6]

union returns every element from either side:

a.union(b)              // {1, 2, 3, 4, 5, 6}

intersection returns only the elements that appear in both:

a.intersection(b)       // {3, 4}

Each method returns a new Set. The original sets stay untouched. Iteration order over the result is not guaranteed, sort before printing.

Challenge

Easy

Read two lines of input. Each is a comma-separated list of integers.

Treat them as sets a and b. Print two lines:

The intersection, sorted ascending, joined with , (or an empty line when empty)
The union, sorted ascending, joined with ,

For input 1,2,3,4 on the first line and 3,4,5,6 on the second, the output is:

3,4
1,2,3,4,5,6

Cheat sheet

Set operations in Swift:

let a: Set = [1, 2, 3, 4]
let b: Set = [3, 4, 5, 6]

a.union(b)         // {1, 2, 3, 4, 5, 6} - elements from either set
a.intersection(b)  // {3, 4} - elements in both sets

Both methods return a new Set; originals are unchanged. Sort before printing since iteration order is not guaranteed.

Try it yourself

let a = Set(readLine()!.components(separatedBy: ",").map { Int($0)! })
let b = Set(readLine()!.components(separatedBy: ",").map { Int($0)! })

// TODO: intersection sorted joined, union sorted joined