feat: add swift implementation to lcof problem: No.15 (doocs#2868)

Author: klever34

lcof/面试题15. 二进制中1的个数/README.md

@@ -147,6 +147,22 @@ var hammingWeight = function (n) {
 };
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func hammingWeight(_ n: Int) -> Int {
+        var n = n
+        var ans = 0
+        while n != 0 {
+            n &= (n - 1)
+            ans += 1
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题15. 二进制中1的个数/Solution.swift

@@ -0,0 +1,11 @@
+class Solution {
+    func hammingWeight(_ n: Int) -> Int {
+        var n = n
+        var ans = 0
+        while n != 0 {
+            n &= (n - 1)
+            ans += 1
+        }
+        return ans
+    }
+}