Revert "optimize Insert() function as review suggestion."

revert to last good code。
This reverts commit adb42e4.

data_structures/binary_search_tree.cpp

@@ -35,12 +35,10 @@ struct node {
  * \param[in] root root node of a tree
  * \param[in] x a node with value to be insert
  */
-void Insert(std::shared_ptr<node>& root, int x) {
-    if (root == nullptr) {
-        root = std::make_shared<node>();
-        root->val = x;
-        root->left = nullptr;
-        root->right = nullptr;
+void Insert(node* root, int x) {
+    if (root == NULL) {
+        std::cout << " \n invalid root node = " << root << std::endl;
+        std::cout << " \n please call Insert() with valid root node!!! \n";
         return;
     }
 
@@ -51,7 +49,7 @@ void Insert(std::shared_ptr<node>& root, int x) {
             root->left->left = nullptr;
             root->left->right = nullptr;
         } else {
-            Insert(root->left, x);
+            Insert(root->left.get(), x);
         }
     } else {
         if (root->right == nullptr) {
@@ -60,7 +58,7 @@ void Insert(std::shared_ptr<node>& root, int x) {
             root->right->left = nullptr;
             root->right->right = nullptr;
         } else {
-            Insert(root->right, x);
+            Insert(root->right.get(), x);
         }
     }
 }
@@ -203,12 +201,12 @@ void test_tree() {
     root->left = nullptr;
     root->right = nullptr;
     // test Insert()
-    data_structure::BST::Insert(root, 2);
-    data_structure::BST::Insert(root, 1);
-    data_structure::BST::Insert(root, 3);
-    data_structure::BST::Insert(root, 6);
-    data_structure::BST::Insert(root, 5);
-    data_structure::BST::Insert(root, 7);
+    data_structure::BST::Insert(root.get(), 2);
+    data_structure::BST::Insert(root.get(), 1);
+    data_structure::BST::Insert(root.get(), 3);
+    data_structure::BST::Insert(root.get(), 6);
+    data_structure::BST::Insert(root.get(), 5);
+    data_structure::BST::Insert(root.get(), 7);
     std::cout
         << "after Insert() ,the expected output should be : 1, 2, 3, 4, 5, 6 ,7"
         << std::endl;
@@ -240,7 +238,13 @@ int main() {
     test_tree();
     int value = 0;
     int ch = 0;
-    std::shared_ptr<data_structure::BST::node> root = nullptr;
+    std::shared_ptr<data_structure::BST::node> root(
+        new data_structure::BST::node);
+    std::cout << "\nEnter the value of root node :";
+    std::cin >> value;
+    root->val = value;
+    root->left = nullptr;
+    root->right = nullptr;
 
     do {
         std::cout << "\n1. Insert"
@@ -258,7 +262,14 @@ int main() {
         case 1:
             std::cout << "\nEnter the value to be Inserted : ";
             std::cin >> x;
-            data_structure::BST::Insert(root, x);
+            if (root.get())
+                data_structure::BST::Insert(root.get(), x);
+            else {
+                root = std::make_shared<data_structure::BST::node>();
+                root->val = x;
+                root->left = nullptr;
+                root->right = nullptr;
+            }
             break;
         case 2:
             std::cout << "\nEnter the value to be Deleted : ";