[String] Optimize syntax for Keyboard Row

Author: soapyigu

README.md

@@ -72,9 +72,9 @@
 ## String
 | Title | Solution | Difficulty | Time | Space |
 | ----- | -------- | ---------- | ---- | ----- |
-[Fizz Buzz](https://leetcode.com/problems/fizz-buzz/)| [Swift](./FizzBuzz.swift)| Easy| O(n)| O(1)|
-[First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/)| [Swift](./FirstUniqueCharacterInString.swift)| Easy| O(n)| O(1)|
-[Keyboard Row](https://leetcode.com/problems/keyboard-row/)| [Swift](./KeyboardRow.swift)| Easy| O(nm)| O(n)|
+[Fizz Buzz](https://leetcode.com/problems/fizz-buzz/)| [Swift](./String/FizzBuzz.swift)| Easy| O(n)| O(1)|
+[First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/)| [Swift](./String/FirstUniqueCharacterInString.swift)| Easy| O(n)| O(1)|
+[Keyboard Row](https://leetcode.com/problems/keyboard-row/)| [Swift](./String/KeyboardRow.swift)| Easy| O(nm)| O(n)|
 [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)| [Swift](./String/ValidPalindrome.swift)| Easy| O(n)| O(n)|
 [Detect Capital](https://leetcode.com/problems/detect-capital/)| [Swift](./String/DetectCapital.swift)| Easy| O(n)| O(1)|
 [Count and Say](https://leetcode.com/problems/count-and-say/)| [Swift](./String/CountAndSay.swift)| Easy| O(n^2)| O(n)|

String/KeyboardRow.swift

@@ -1,6 +1,6 @@
 /**
  * Question Link: https://leetcode.com/problems/keyboard-row/
- * Primary idea: Convert each row to set to determine the word is subset or not.
+ * Primary idea: Use filter to determine the word is subset or not.
  * 
  * Note: You can also use intersect() or union() functions to solve this problem.
  *
@@ -10,26 +10,14 @@
 
 class KeyboardRow {
     func findWords(_ words: [String]) -> [String] {
-        var res = [String]()
-  
-        let rowOne = Set("qwertyuiop".characters), rowTwo = Set("asdfghjkl".characters), rowThree = Set("zxcvbnm".characters)
-  
-        for word in words {
-            if isInRow(word, rowOne) || isInRow(word, rowTwo) || isInRow(word, rowThree) {
-                res.append(word)
-            }
-        } 
-  
-        return res
+        let rowOne = "qwertyuiop", rowTwo = "asdfghjkl", rowThree = "zxcvbnm"
+
+        return words.filter { word in rowOne.contains(word) || rowTwo.contains(word) || rowThree.contains(word) }
     }
-    
-    fileprivate func isInRow(_ word: String, _ row: Set<Character>) -> Bool {
-        for char in word.lowercased().characters {
-            if !row.contains(char) {
-                return false
-            }
+
+    extension String {
+        func contains(_ word: String) -> Bool {
+            return word.filter { c in !self.contains(c) }.characters.count == 0
         }
-  
-        return true
     }
 }