Add solution 500

Author: vulgur

500_KeyboardRow.swift

@@ -0,0 +1,43 @@
+class Solution {
+    let row1 = "qwertyuiopQWERTYUIOP"
+    let row2 = "asdfghjklASDFGHJKL"
+    let row3 = "zxcvbnm(ZXCVBNM)"
+    
+    private func row(of letter: String) -> Int {
+        if row1.contains(letter) {
+            return 1
+        } else if row2.contains(letter) {
+            return 2
+        } else if row3.contains(letter) {
+            return 3
+        } else {
+            return 0
+        }
+    }
+    private func canTypeInRow(_ word: String) -> Bool {
+        let firstLetter = String(word.first!)
+        let firstLetterRow = row(of: firstLetter)
+        let startIndex = word.index(after: word.startIndex)
+        for item in word[startIndex...] {
+            let letter = String(item)
+            let row = self.row(of: letter)
+            if row != firstLetterRow || row == 0 {
+                return false
+            }
+        }
+        return true
+    }
+    func findWords(_ words: [String]) -> [String] {
+        
+        var results = [String]()
+        for word in words {
+            if word.isEmpty {
+                continue
+            }
+            if canTypeInRow(word) {
+                results.append(word)
+            }
+        }
+        return results
+    }
+}