Add dart chapter_computational_complexity (#363)

* add dart chapter_array_and_linkedlist

* update my_list.dart

* update chapter_array_and_linkedlist

* Update my_list.dart

* Update array.dart

* Update file name

* Add chapter_computational_complexity

* Add chapter_computational_complexity

* add space_complexity class and format code

* remove class

---------

Co-authored-by: huangjianqing <huangjianqing@52tt.com>
Co-authored-by: Yudong Jin <krahets@163.com>

codes/dart/utils/tree_node.dart

@@ -0,0 +1,69 @@
+/**
+ * File: tree_node.dart
+ * Created Time: 2023-2-12
+ * Author: Jefferson (JeffersonHuang77@gmail.com)
+ */
+
+import 'dart:collection';
+
+class TreeNode {
+  late int val; // 结点值
+  late int height; // 结点高度
+  late TreeNode? left; // 左子结点引用
+  late TreeNode? right; // 右子结点引用
+
+  TreeNode(int x) {
+    val = x;
+  }
+}
+
+/**
+     * Generate a binary tree given an array
+     * @param list
+     * @return
+     */
+TreeNode? listToTree(List<int> list) {
+  int size = list.length;
+  if (size == 0) return null;
+
+  TreeNode root = TreeNode(list[0]);
+  Queue<TreeNode?> queue = Queue();
+  queue.add(root);
+  int i = 0;
+  while (!queue.isEmpty) {
+    TreeNode? node = queue.first;
+    queue.removeFirst();
+    if (++i >= size) break;
+    node?.left = TreeNode(list[i]);
+    queue.add(node?.left);
+    if (++i >= size) break;
+    node?.left = TreeNode(list[i]);
+    queue.add(node?.right);
+  }
+  return root;
+}
+
+/**
+     * Serialize a binary tree to a list
+     * @param root
+     * @return
+     */
+List<int?> treeToList(TreeNode? root) {
+  List<int?> list = [];
+  if (root == null) return list;
+  Queue<TreeNode?> queue = Queue();
+  queue.add(root);
+
+  while (!queue.isEmpty) {
+    TreeNode? node = queue.first;
+    queue.removeFirst();
+    if (node != null) {
+      list.add(node.val);
+      queue.add(node.left);
+      queue.add(node.right);
+    } else {
+      list.add(null);
+    }
+  }
+  return list;
+}