[Math] fix solutions for Palindrome Number, Single Number II, and Sum…

… Two Integers

Math/PalindromeNumber.swift

@@ -4,23 +4,30 @@
  *
  * Time Complexity: O(1), Space Complexity: O(1)
  */
- class Solution {
+
+ class PalindromeNumber {
     func isPalindrome(x: Int) -> Bool {
-        if x < 0 {
+        guard x >= 0 else {
             return false
         }
 
-        var chars: [Character] = [Character](String(x).characters)
-        var b = 0
-        var e = chars.count - 1
+        var x = x
+        var div = 1
 
-        while b < e {
-            if chars[b] != chars[e] {
+        while (x / div >= 10) {
+            div = div * 10
+        }
+
+        while (x > 0) {
+            var left = x / div
+            var right = x % 10
+
+            if (left != right) {
                 return false
             }
 
-            b += 1
-            e -= 1
+            x = (x % div) / 10
+            div = div / 100
         }
 
         return true

Math/SingleNumberII.swift

@@ -10,10 +10,11 @@
  *
  */
 
-class Solution {
+class SingleNumberII {
     func singleNumber(nums: [Int]) -> Int {
         var ans = 0
         var sum = 0
+
         for i in 0 ..< 64 {
             sum = 0
             let tmp = (1 << i)

Math/SumTwoIntegers.swift

@@ -16,38 +16,4 @@ class SumTwoIntegers {
         }
         return a
     }
-}
-
-
-/**
- * Question Link: https://leetcode.com/problems/sum-of-two-integers/
- * Primary idea: using ^ instead of +.
- *               00 + 00 <-> ret
- *               01 + 01 <-> ret ^ 10
- *               01 + 00 <-> if ret & 01 != 0
- *                               ret ^ 11
- *                           else
- *                               ret ^ 01
- *
- * Time Complexity: O(1), Space Complexity: O(1)
- */
-
- class Solution {
-    func getSum(a: Int, _ b: Int) -> Int {
-      var ret = 0;
-      for i in 0 ..< 64 {
-          let tmp = 1 << i
-          if a & tmp == 0 && b & tmp == 0 {
-              continue
-          } else if a & tmp != 0 && b & tmp != 0 {
-              ret = ret ^ (tmp << 1)
-          } else {
-              if ret & tmp != 0 {
-                  ret ^= (tmp << 1)
-              }
-              ret ^= tmp
-          }
-      }
-      return ret
-    }
-}
+}