Add Kotlin code for computational complexity (#1090)

* feat(kotlin):new kotlin support files

* fix(kotlin):

    reviewed the formatting, comments and so on.

* fix(kotlin): fix the indentation and format

* feat(kotlin): Add kotlin code for the backtraking chapter.

* fix(kotlin): fix incorrect output of preorder_traversal_iii_template.kt file

* fix(kotlin): simplify kotlin codes

* fix(kotlin): modify n_queens.kt for consistency.

* feat(kotlin): add kotlin code for computational complexity.

* fix(kotlin): remove iteration folder.

* fix(kotlin): remove n_queens.kt file out of folder.

* fix(kotlin): remove some folders.

* style(kotlin): modified two chapters.

codes/kotlin/chapter_computational_complexity/recursion.kt

@@ -0,0 +1,76 @@
+/**
+ * File: recursion.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_computational_complexity.recursion
+
+import java.util.*
+
+/* 递归 */
+fun recur(n: Int): Int {
+    // 终止条件
+    if (n == 1)
+        return 1
+    // 递: 递归调用
+    val res = recur(n - 1)
+    // 归: 返回结果
+    return n + res
+}
+
+/* 使用迭代模拟递归 */
+fun forLoopRecur(n: Int): Int {
+    // 使用一个显式的栈来模拟系统调用栈
+    val stack = Stack<Int>()
+    var res = 0
+    // 递: 递归调用
+    for (i in n downTo 0) {
+        stack.push(i)
+    }
+    // 归: 返回结果
+    while (stack.isNotEmpty()) {
+        // 通过“出栈操作”模拟“归”
+        res += stack.pop()
+    }
+    // res = 1+2+3+...+n
+    return res
+}
+
+/* Kotlin tailrec 关键词使函数实现尾递归优化 */
+tailrec fun tailRecur(n: Int, res: Int): Int {
+    // 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 */
+fun 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)
+    val res = fib(n - 1) + fib(n - 2)
+    // 返回结果 f(n)
+    return res
+}
+
+/* Driver Code */
+fun main() {
+    val n = 5
+    var res: Int
+
+    res = recur(n)
+    println("\n递归函数的求和结果 res = $res")
+
+    res = forLoopRecur(n)
+    println("\n使用迭代模拟递归求和结果 res = $res")
+
+    res = tailRecur(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")
+}