Burrows–Wheeler transform: Difference between revisions

=={{header|Swift}}==

{{trans|Kotlin}}

<lang swift>import Foundation

private let stx = "\u{2}"

private let etx = "\u{3}"

func bwt(_ str: String) -> String? {

guard !str.contains(stx), !str.contains(etx) else {

return nil

}

let ss = stx + str + etx

let table = ss.indices.map({i in ss[i...] + ss[ss.startIndex..<i] }).sorted()

return String(table.map({str in str.last!}))

}

func ibwt(_ str: String) -> String? {

let len = str.count

var table = Array(repeating: "", count: len)

for _ in 0..<len {

for i in 0..<len {

table[i] = String(str[str.index(str.startIndex, offsetBy: i)]) + table[i]

}

table.sort()

}

for row in table where row.hasSuffix(etx) {

return String(row.dropFirst().dropLast())

}

return nil

}

func readableBwt(_ str: String) -> String {

return str.replacingOccurrences(of: "\u{2}", with: "^").replacingOccurrences(of: "\u{3}", with: "|")

}

let testCases = [

"banana",

"appellee",

"dogwood",

"TO BE OR NOT TO BE OR WANT TO BE OR NOT?",

"SIX.MIXED.PIXIES.SIFT.SIXTY.PIXIE.DUST.BOXES",

"\u{2}ABC\u{3}"

]

for test in testCases {

let b = bwt(test) ?? "error"

let c = ibwt(b) ?? "error"

print("\(readableBwt(test)) -> \(readableBwt(b)) -> \(readableBwt(c))")

}</lang>

{{out}}

<pre>banana -> |annb^aa -> banana

appellee -> |e^elplepa -> appellee

dogwood -> |do^oodwg -> dogwood

TO BE OR NOT TO BE OR WANT TO BE OR NOT? -> |?OOORREEETTRTW BBB ATTT NNOOONOO^ -> TO BE OR NOT TO BE OR WANT TO BE OR NOT?

SIX.MIXED.PIXIES.SIFT.SIXTY.PIXIE.DUST.BOXES -> |STEXYDST.E.IXXIIXXSSMPPS.B..EE.^.USFXDIIOIIIT -> SIX.MIXED.PIXIES.SIFT.SIXTY.PIXIE.DUST.BOXES

^ABC| -> error -> error</pre>