feat: add rust codes for chapter computational complexity (#714)

codes/rust/chapter_computational_complexity/recursion.rs

@@ -0,0 +1,55 @@
+/*
+ * File: recursion.rs
+ * Created Time: 2023-09-02
+ * Author: night-cruise (2586447362@qq.com)
+ */
+
+
+/* 递归 */
+fn recur(n: i32) -> i32 {
+    // 终止条件
+    if n == 1 {
+        return 1;
+    }
+    // 递：递归调用
+    let res = recur(n - 1);
+    // 归：返回结果
+    n + res
+}
+
+/* 尾递归 */
+fn tail_recur(n: i32, res: i32) -> i32 {
+    // 终止条件
+    if n == 0 {
+        return res;
+    }
+    // 尾递归调用
+    tail_recur(n - 1, res + n)
+}
+
+/* 斐波那契数列：递归 */
+fn fib(n: i32) -> i32 {
+    // 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 - 1) + fib(n - 2);
+    // 返回结果
+    res
+}
+
+/* Driver Code */
+fn main() {
+    let n = 5;
+    let mut res;
+
+    res = recur(n);
+    println!("\n递归函数的求和结果 res = {res}");
+
+    res = tail_recur(n, 0);
+    println!("\n尾递归函数的求和结果 res = {res}");
+    
+    res = fib(n);
+    println!("\n斐波那契数列的第 {n} 项为 {res}");
+}