Smart TV Virtual Keyboard Trace

tv.swift

struct Coordinate {
    var row: Int = 0
    var col: Int = 0
}

var coordinateMapping: [Character: Coordinate] = {
    var mapping: [Character: Coordinate] = [:]
    for (index, letter) in "ABCDEFGHIJKLMNOPQRSTUVWXYZ".enumerated() {
        mapping[letter] = Coordinate(row: index / 5, col: index % 5)
    }
    return mapping
}()
    
func instructions(for word: String) -> String? {
    var result: String = ""
    guard var current: Coordinate = coordinateMapping["A"] else {
        return nil
    }
    for letter in word.uppercased() {
        guard let target: Coordinate = coordinateMapping[letter] else {
            return nil
        }
        // Order matters, must do L before D and must do U before R
        result += String(repeating: "L", count: max(current.col - target.col, 0))
        result += String(repeating: "D", count: max(target.row - current.row, 0))
        result += String(repeating: "U", count: max(current.row - target.row, 0))
        result += String(repeating: "R", count: max(target.col - current.col, 0))
        result += "E"
        current = target
    }
    return result
}

assert(instructions(for: "A") == "E")
assert(instructions(for: "BAT") == "RELEDDDRRRRE")
assert(instructions(for: "8rh4") == nil)
assert(instructions(for: "Zoo") == "DDDDDEUUURRRREE")
assert(instructions(for: "hazy") == "DRRELLUEDDDDDEURRRRE")
print("All tests passed")

Great job!