feat: add swift implementation to lcof problem: No.14.2 (doocs#2867)

Author: klever34

lcof/面试题14- II. 剪绳子 II/README.md

@@ -232,6 +232,41 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    private let mod = 1000000007
+
+    func cuttingRope(_ n: Int) -> Int {
+        if n < 4 {
+            return n - 1
+        }
+        if n % 3 == 0 {
+            return qpow(3, n / 3)
+        }
+        if n % 3 == 1 {
+            return (4 * qpow(3, n / 3 - 1)) % mod
+        }
+        return (2 * qpow(3, n / 3)) % mod
+    }
+
+    private func qpow(_ a: Int, _ n: Int) -> Int {
+        var a = a
+        var n = n
+        var ans: Int = 1
+        while n > 0 {
+            if (n & 1) == 1 {
+                ans = (ans * a) % mod
+            }
+            a = (a * a) % mod
+            n >>= 1
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题14- II. 剪绳子 II/Solution.swift

@@ -0,0 +1,30 @@
+class Solution {
+    private let mod = 1000000007
+
+    func cuttingRope(_ n: Int) -> Int {
+        if n < 4 {
+            return n - 1
+        }
+        if n % 3 == 0 {
+            return qpow(3, n / 3)
+        }
+        if n % 3 == 1 {
+            return (4 * qpow(3, n / 3 - 1)) % mod
+        }
+        return (2 * qpow(3, n / 3)) % mod
+    }
+
+    private func qpow(_ a: Int, _ n: Int) -> Int {
+        var a = a
+        var n = n
+        var ans: Int = 1
+        while n > 0 {
+            if (n & 1) == 1 {
+                ans = (ans * a) % mod
+            }
+            a = (a * a) % mod
+            n >>= 1
+        }
+        return ans
+    }
+}