Add solution for Reverse Integer

Math/ReverseInteger.swift

@@ -0,0 +1,29 @@
+/**
+ * Question Link: https://leetcode.com/problems/reverse-integer/
+ * Primary idea: Return 0 is the reversal number exceeds the Int32 range.
+ * Time Complexity: O(1)
+ */
+
+ class Solution {
+    func reverse(x: Int) -> Int {
+        if x < 0 {
+            return 0 - reverse(0 - x)
+        }
+
+        var carry = 1
+        var ret = 0
+        for c in String(x).characters {
+            let someString = String(c)
+            if let someInt = Int(someString) {
+                ret += someInt * carry
+                carry *= 10
+            }
+        }
+
+        if ret > Int(Int32.max) || ret < Int(Int32.min) {
+            return 0
+        }
+
+        return ret
+    }
+}