Run-length encoding: Difference between revisions

</pre>

=={{header|Swift}}==

Using array as internal representation of encoded input:

<lang swift>import Foundation

// "WWWBWW" -> [(3, W), (1, B), (2, W)]

func encode(input: String) -> [(Int, Character)] {

return input.characters.reduce([(Int, Character)]()) {

if $0.last?.1 == $1 { var r = $0; r[r.count - 1].0++; return r }

return $0 + [(1, $1)]

}

}

// [(3, W), (1, B), (2, W)] -> "WWWBWW"

func decode(encoded: [(Int, Character)]) -> String {

return encoded.reduce("") { $0 + String(count: $1.0, repeatedValue: $1.1) }

}

</lang>

'''Usage:'''

<lang swift>

let input = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"

let output = decode(encode(input))

print(output == input)

</lang>

{{Out}}

<pre>true</pre>

Converting encoded array into the string and then decoding it using NSScanner:

<lang swift>// "3W1B2W" -> "WWWBWW"

func decode(encoded: String) -> String {

let scanner = NSScanner(string: encoded)

var char: NSString? = nil

var count: Int = 0

var out = ""

while scanner.scanInteger(&count) {

while scanner.scanCharactersFromSet(NSCharacterSet.letterCharacterSet(), intoString: &char) {

out += String(count: count, repeatedValue: Character(char as! String))

}

}

return out

}

</lang>

<lang swift>let encodedString = encode(input).reduce("") { $0 + "\($1.0)\($1.1)" }

print(encodedString)

let outputString = decode(encodedString)

print(outputString == input)

</lang>

{{Out}}

<pre>

12W1B12W3B24W1B14W

true