feat: Add Dart Codes for section_iteration_and_recursion (#696)

codes/dart/chapter_computational_complexity/recursion.dart

@@ -0,0 +1,48 @@
+/**
+ * File: recursion.dart
+ * Created Time: 2023-08-27
+ * Author: liuyuxin (gvenusleo@gmail.com)
+ */
+
+/* 递归 */
+int recur(int n) {
+  // 终止条件
+  if (n == 1) return 1;
+  // 递：递归调用
+  int res = recur(n - 1);
+  // 归：返回结果
+  return n + res;
+}
+
+/* 尾递归 */
+int tailRecur(int n, int res) {
+  // 终止条件
+  if (n == 0) return res;
+  // 尾递归调用
+  return tailRecur(n - 1, res + n);
+}
+
+/* 斐波那契数列：递归 */
+int fib(int n) {
+  // 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)
+  int res = fib(n - 1) + fib(n - 2);
+  // 返回结果 f(n)
+  return res;
+}
+
+/* Driver Code */
+void main() {
+  int n = 5;
+  int res;
+
+  res = recur(n);
+  print("\n递归函数的求和结果 res = $res");
+
+  res = tailRecur(n, 0);
+  print("\n尾递归函数的求和结果 res = $res");
+
+  res = fib(n);
+  print("\n斐波那契数列的第 $n 项为 $res");
+}