feat: add swift implementation to lcof problem: No.16 (doocs#2869)

Author: klever34

lcof/面试题16. 数值的整数次方/README.md

@@ -237,6 +237,32 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func myPow(_ x: Double, _ n: Int) -> Double {
+        return n >= 0 ? qpow(x, Int64(n)) : 1 / qpow(x, -Int64(n))
+    }
+
+    private func qpow(_ a: Double, _ n: Int64) -> Double {
+        var ans: Double = 1
+        var base: Double = a
+        var exponent: Int64 = n
+
+        while exponent > 0 {
+            if (exponent & 1) == 1 {
+                ans *= base
+            }
+            base *= base
+            exponent >>= 1
+        }
+
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题16. 数值的整数次方/Solution.swift

@@ -0,0 +1,21 @@
+class Solution {
+    func myPow(_ x: Double, _ n: Int) -> Double {
+        return n >= 0 ? qpow(x, Int64(n)) : 1 / qpow(x, -Int64(n))
+    }
+
+    private func qpow(_ a: Double, _ n: Int64) -> Double {
+        var ans: Double = 1
+        var base: Double = a
+        var exponent: Int64 = n
+        
+        while exponent > 0 {
+            if (exponent & 1) == 1 {
+                ans *= base
+            }
+            base *= base
+            exponent >>= 1
+        }
+        
+        return ans
+    }
+}