How can I expand a Dict(string, array) in Swift 5

Question

Can I expand the dictionary to an array of pairs in Swift 5 using map/reduce or will I have to do a for each ?

let dict = ["A": ["1","2","3","4"],
            "B": ["5","6","7","8"]]

???

//result = [["A", "1"],["A", "2"],....["B", "5"],....]

Answer 1

let result = dict.map { (letter: String, digits: [String]) in
    return digits.map { digit in
        return [letter, digit]
    }
}.reduce([]) {
    $0 + $1
}

Answer 2

This one is shortest solution.

let result = dict.map { dic in
        dic.value.map { [dic.key : $0] }
    }.reduce([], +) 

Answer 3

Here's a solution that doesn't need reduce :

let dict = ["A": ["1","2","3","4"],
            "B": ["5","6","7","8"]]
let result = dict.map { kv in kv.value.map { [kv.key, $0] } }.flatMap { $0 }