HackerRank Encryption

hackerrank-encryption.swift

guard let response = readLine(stripNewline: true) else {
    fatalError("Expecting input!")
}
let withoutSpaces = response.characters.filter { $0 != " " }

let length  = withoutSpaces.count
let minRows = Int(floor(sqrt(Double(length))))
let columns = minRows * minRows >= length ? minRows : minRows + 1

var output = ""
output.reserveCapacity(length + columns)

for offset in 0 ..< columns {
    let startIndex = withoutSpaces.startIndex.advancedBy(offset)
    for index in startIndex.stride(to: withoutSpaces.endIndex, by: columns) {
        output.append(withoutSpaces[index])
    }
    output.append(Character(" "))
}

print(output)