Add solution for palindrome number

Author: Charlene Jiang

Math/PalindromeNumber.swift

@@ -0,0 +1,28 @@
+/**
+ * Question Link: https://leetcode.com/problems/palindrome-number/
+ * Primary idea: Negative numbers are not palindromes.
+ *
+ * Time Complexity: O(1), Space Complexity: O(1)
+ */
+ class Solution {
+    func isPalindrome(x: Int) -> Bool {
+        if x < 0 {
+            return false
+        }
+        
+        var chars: [Character] = [Character](String(x).characters)
+        var b = 0
+        var e = chars.count - 1
+        
+        while b < e {
+            if chars[b] != chars[e] {
+                return false
+            }
+            
+            b += 1
+            e -= 1
+        }
+        
+        return true
+    }
+}

README.md

@@ -618,7 +618,7 @@
 |		|	12	|	[Integer to Roman](https://oj.leetcode.com/problems/integer-to-roman/)	|	♥    ♥	|
 |		|	11	|	[Container With Most Water](https://oj.leetcode.com/problems/container-with-most-water/)	|	♥    ♥	|
 |		|	10	|	[Regular Expression Matching](https://oj.leetcode.com/problems/regular-expression-matching/)	|	♥    ♥    ♥	|
-|		|	9	|	[Palindrome Number](https://oj.leetcode.com/problems/palindrome-number/)	|	♥	|
+|	[Swift](./Math/PalindromeNumber.swift)	|	9	|	[Palindrome Number](https://oj.leetcode.com/problems/palindrome-number/)	|	♥	|
 |	[Swift](./Math/Atoi.swift)	|	8	|	[String to Integer (atoi)](https://oj.leetcode.com/problems/string-to-integer-atoi/)	|	♥	|
 |	[Swift](./Math/ReverseInteger.swift)	|	7	|	[Reverse Integer](https://oj.leetcode.com/problems/reverse-integer/)	|	♥	|
 |	[Swift](./String/ZigZagConversion.swift)	|	6	|	[ZigZag Conversion](https://oj.leetcode.com/problems/zigzag-conversion/)	|	♥	|