feat: add swift implementation to lcof2 problem: No.003 (doocs#2967)

Author: klever34

lcof2/剑指 Offer II 003. 前 n 个数字二进制中 1 的个数/README.md

@@ -144,6 +144,23 @@ function countBits(n: number): number[] {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func countBits(_ n: Int) -> [Int] {
+        if n == 0 {
+            return [0]
+        }
+        var f = [Int](repeating: 0, count: n + 1)
+        for i in 1...n {
+            f[i] = f[i & (i - 1)] + 1
+        }
+        return f
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 003. 前 n 个数字二进制中 1 的个数/Solution.swift

@@ -0,0 +1,12 @@
+class Solution {
+    func countBits(_ n: Int) -> [Int] {
+        if n == 0 {
+            return [0]
+        }
+        var f = [Int](repeating: 0, count: n + 1)
+        for i in 1...n {
+            f[i] = f[i & (i - 1)] + 1
+        }
+        return f
+    }
+}