[Math] Add a solution to Integer to English Words, and update Add Bin…

…ary to Swift 3.0

Math/AddBinary.swift

@@ -9,32 +9,24 @@
  */
 
 class AddBinary {
-    func addBinary(a: String, _ b: String) -> String {
-        var res = ""
-        var aChars = [Character](a.characters)
-        var bChars = [Character](b.characters)
-
-        var i = aChars.count - 1
-        var j = bChars.count - 1
-        var carry = 0
-        var num = 0
+    func addBinary(_ a: String, _ b: String) -> String {
+        var sum = 0, carry = 0, res = ""
+        let aChars = Array(a.characters), bChars = Array(b.characters)
+        var i = aChars.count - 1, j = bChars.count - 1
 
         while i >= 0 || j >= 0 || carry > 0 {
-            num = carry
-
+            sum = carry
             if i >= 0 {
-                num += Int(String(aChars[i]))!
+                sum += Int(String(aChars[i]))!
                 i -= 1
             }
             if j >= 0 {
-                num += Int(String(bChars[j]))!
+                sum += Int(String(bChars[j]))!
                 j -= 1
             }
-
-            carry = num / 2
-            num = num % 2
-
-            res = String(num) + res
+            carry = sum / 2
+            sum = sum % 2
+            res = String(sum) + res
         }
 
         return res

Math/IntegerEnglishWords.swift

@@ -0,0 +1,48 @@
+/**
+ * Question Link: https://leetcode.com/problems/integer-to-english-words/
+ * Primary idea: Divide and mod 1000, 100, and 10 to get string for each digit
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+
+class IntegerEnglishWords {
+    func numberToWords(_ num: Int) -> String {
+        let l1 = ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
+        let l2 = ["Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
+        let l3 = "Hundred"
+        let l4 = ["Thousand", "Million", "Billion"]
+        var res = "", num = num, digit = -1
+
+        if num == 0 {
+            return "Zero"
+        }
+
+        while num > 0 {
+            var temp = "", token = num % 1000
+
+            if token > 99 {
+                temp += "\(l1[token / 100]) \(l3) "
+                token %= 100
+            }
+
+            if token > 19 {
+                temp += "\(l2[token / 10 - 2]) "
+                token %= 10
+            }
+
+            if token > 0 {
+                temp += "\(l1[token]) "
+            }
+
+            if digit != -1 && temp != "" {
+                res = temp + l4[digit] + " " + res
+            } else {
+                res = temp + res
+            }
+            digit += 1
+            num /= 1000
+        }
+
+        return String(res.characters.dropLast())
+    }
+}