@@ -1,4 +1,4 @@
-// last checked with Xcode 9.0b4
+// last checked with Xcode 11.4
 #if swift(>=4.0)
 print("Hello, Swift 4!")
 #endif
@@ -7,10 +7,10 @@ extension String {
 public func longestCommonSubsequence(_ other: String) -> String {
 
 func lcsLength(_ other: String) -> [[Int]] {
-var matrix = [[Int]](repeating: [Int](repeating: 0, count: other.characters.count+1), count: self.characters.count+1)
+var matrix = [[Int]](repeating: [Int](repeating: 0, count: other.count+1), count: self.count+1)
 
-for (i, selfChar) in self.characters.enumerated() {
-for (j, otherChar) in other.characters.enumerated() {
+for (i, selfChar) in self.enumerated() {
+for (j, otherChar) in other.enumerated() {
 if otherChar == selfChar {
 matrix[i+1][j+1] = matrix[i][j] + 1
 } else {
@@ -22,8 +22,8 @@ extension String {
 }
 
 func backtrack(_ matrix: [[Int]]) -> String {
-var i = self.characters.count
-var j = other.characters.count
+var i = self.count
+var j = other.count
 var charInSequence = self.endIndex
 
 var lcs = String()
@@ -41,7 +41,7 @@ extension String {
 lcs.append(self[charInSequence])
 }
 }
-return String(lcs.characters.reversed())
+return String(lcs.reversed())
 }
 
 return backtrack(lcsLength(other))