feat: add swift implementation to lcof problem: No.65 (doocs#2960)

Author: klever34

lcof/面试题65. 不用加减乘除做加法/README.md

@@ -159,6 +159,23 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func add(_ a: Int, _ b: Int) -> Int {
+        var a = a
+        var b = b
+        while b != 0 {
+            let c = (a & b) << 1
+            a ^= b
+            b = c
+        }
+        return a
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题65. 不用加减乘除做加法/Solution.swift

@@ -0,0 +1,12 @@
+class Solution {
+    func add(_ a: Int, _ b: Int) -> Int {
+        var a = a
+        var b = b
+        while b != 0 {
+            let c = (a & b) << 1
+            a ^= b
+            b = c
+        }
+        return a
+    }
+}