Merge branch 'master' of github.com:soapyigu/LeetCode_Swift

Author: Charlene Jiang

Math/SumTwoIntegers.swift

@@ -16,4 +16,38 @@ 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
+    }
+}

README.md

@@ -10,4 +10,28 @@ class ReverseString {
     func reverseString(s: String) -> String {
         return String(s.characters.reverse())
     }
-}
+}
+
+/**
+ * Question Link: https://leetcode.com/problems/reverse-string/
+ * Primary idea: Using two iterators, one at the beginning, moving forward, another at the end moving backward.
+ *               Swap them each time they move.
+ * 
+ * Time Complexity: O(n), Space Complexity: O(1)
+ *
+ */
+class Solution {
+    func reverseString(s: String) -> String {
+        var chars: [Character] = [Character](s.characters)
+        var b = 0
+        var e = chars.count - 1
+        while b < e {
+            let tmp = chars[b]
+            chars[b] = chars[e]
+            chars[e] = tmp
+            b += 1
+            e -= 1
+        }
+        return String(chars)
+    }
+}