Update Z-Algorithm up to Swift 4.2.

Author: artFintch

Z-Algorithm/README.markdown

@@ -28,8 +28,7 @@ This a simple description of the idea that is behind this algorithm. There are a
 Here is the code of the function that computes the Z-array:
 ```swift
 func ZetaAlgorithm(ptrn: String) -> [Int]? {
-
-    let pattern = Array(ptrn.characters)
+    let pattern = Array(ptrn)
     let patternLength: Int = pattern.count
 
     guard patternLength > 0 else {
@@ -131,7 +130,7 @@ The Z-Algorithm discussed above leads to the simplest linear-time string matchin
 extension String {
 
     func indexesOf(pattern: String) -> [Int]? {
-        let patternLength: Int = pattern.characters.count
+        let patternLength: Int = pattern.count
         /* Let's calculate the Z-Algorithm on the concatenation of pattern and text */
         let zeta = ZetaAlgorithm(ptrn: pattern + "💲" + self)
 

Z-Algorithm/ZAlgorithm.swift

@@ -9,8 +9,7 @@
 import Foundation
 
 func ZetaAlgorithm(ptrn: String) -> [Int]? {
-
-  let pattern = Array(ptrn.characters)
+  let pattern = Array(ptrn)
   let patternLength = pattern.count
 
   guard patternLength > 0 else {

Z-Algorithm/ZetaAlgorithm.playground/Contents.swift

@@ -1,13 +1,7 @@
 //: Playground - noun: a place where people can play
 
-// last checked with Xcode 9.0b4
-#if swift(>=4.0)
-print("Hello, Swift 4!")
-#endif
-
 func ZetaAlgorithm(ptrn: String) -> [Int]? {
-
-  let pattern = Array(ptrn.characters)
+  let pattern = Array(ptrn)
   let patternLength = pattern.count
 
   guard patternLength > 0 else {
@@ -65,7 +59,7 @@ func ZetaAlgorithm(ptrn: String) -> [Int]? {
 extension String {
 
   func indexesOf(pattern: String) -> [Int]? {
-    let patternLength = pattern.characters.count
+    let patternLength = pattern.count
     let zeta = ZetaAlgorithm(ptrn: pattern + "💲" + self)
 
     guard zeta != nil else {

Z-Algorithm/ZetaAlgorithm.swift

@@ -11,7 +11,7 @@ import Foundation
 extension String {
 
   func indexesOf(pattern: String) -> [Int]? {
-    let patternLength = pattern.characters.count
+    let patternLength = pattern.count
     let zeta = ZetaAlgorithm(ptrn: pattern + "💲" + self)
 
     guard zeta != nil else {