Initial data commit

Task/Burrows-Wheeler-transform/Swift/burrows-wheeler-transform.swift

@@ -0,0 +1,55 @@
+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))")
+}