feat: add Swift codes for iteration_and_recursion article (#717)

codes/swift/chapter_computational_complexity/recursion.swift

@@ -0,0 +1,57 @@
+/**
+ * File: recursion.swift
+ * Created Time: 2023-09-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 递归 */
+func recur(n: Int) -> Int {
+    // 终止条件
+    if n == 1 {
+        return 1
+    }
+    // 递：递归调用
+    let res = recur(n: n - 1)
+    // 归：返回结果
+    return n + res
+}
+
+/* 尾递归 */
+func tailRecur(n: Int, res: Int) -> Int {
+    // 终止条件
+    if n == 0 {
+        return res
+    }
+    // 尾递归调用
+    return tailRecur(n: n - 1, res: res + n)
+}
+
+/* 斐波那契数列：递归 */
+func fib(n: Int) -> Int {
+    // 终止条件 f(1) = 0, f(2) = 1
+    if n == 1 || n == 2 {
+        return n - 1
+    }
+    // 递归调用 f(n) = f(n-1) + f(n-2)
+    let res = fib(n: n - 1) + fib(n: n - 2)
+    // 返回结果 f(n)
+    return res
+}
+
+@main
+enum Recursion {
+    /* Driver Code */
+    static func main() {
+        let n = 5
+        var res = 0
+
+        res = recursion.recur(n: n)
+        print("\n递归函数的求和结果 res = \(res)")
+
+        res = recursion.tailRecur(n: n, res: 0)
+        print("\n尾递归函数的求和结果 res = \(res)")
+
+        res = recursion.fib(n: n)
+        print("\n斐波那契数列的第 \(n) 项为 \(res)")
+    }
+}