Merge pull request #1 from DarkSatyr/Null-condition-fix

Fixed crash on condition when at least 1 string is empty

Author: TheDarkCode

SwiftyLevenshtein.swift

@@ -137,11 +137,13 @@ public struct Array2D {
 
 public func slowlevenshtein(sourceString: String, target targetString: String) -> Int {
 
+    let targetLength = targetString.characters.count
+    let sourceLength = sourceString.characters.count
+    guard targetLength > 0 && sourceLength > 0 else { return max(targetLength, sourceLength) }
+    
     let source = Array(sourceString.unicodeScalars)
     let target = Array(targetString.unicodeScalars)
 
-    let (sourceLength, targetLength) = (source.count, target.count)
-    
     var matrix = Array(count: targetLength + 1, repeatedValue: Array(count: sourceLength + 1, repeatedValue: 0))
 
     for x in  1..<targetLength {
@@ -176,11 +178,13 @@ public func slowlevenshtein(sourceString: String, target targetString: String) -
 
 public func levenshtein(sourceString: String, target targetString: String) -> Int {
 
+    let targetLength = targetString.characters.count
+    let sourceLength = sourceString.characters.count
+    guard targetLength > 0 && sourceLength > 0 else { return max(targetLength, sourceLength) }
+    
     let source = Array(sourceString.unicodeScalars)
     let target = Array(targetString.unicodeScalars)
 
-    let (sourceLength, targetLength) = (source.count, target.count)
-    
     var distance = Array2D(columns: sourceLength + 1, rows: targetLength + 1)
 
     for x in 1...sourceLength {