difficulty inserting into binary search tree - c++

Question

I am currently learning C++ and have been researching BST. I took upon myself a task within a workbook but have been struggling to finish the implementation.
I am not allowed to change the header file or any of the function definitions but I am allowed to add helpers.
I have attempted adding some helpers, but whenever I run the test file, no words are inserted into the tree.
I was hoping someone would be able to help me or give me guidance on finishing the implementation.
Any help on the other functions would be greatly appreciated!
My Header File:
#pragma once
#include <iostream>
#include <string>
// Node of the tree
struct Node
{
std::string data;
Node *left = nullptr;
Node *right = nullptr;
};
class BST
{
private:
Node *root = nullptr;
public:
BST();
BST(std::string word);
BST(const BST &rhs);
~BST();
void insert(std::string word);
void remove(std::string word);
bool exists(std::string word) const;
std::string inorder() const;
std::string preorder() const;
std::string postorder() const;
bool operator==(const BST &other) const;
bool operator!=(const BST &other) const;
};
My BST file:
#include "bst.h"
#include <iostream>
#include <string>
using namespace std;
string HelperInsert(Node **root, std::string word)
{
if (*root == nullptr)
{
// Create new node
*root = new Node;
// Set new value
(*root)->data = word;
// Set branches to nullptr
(*root)->left = nullptr;
(*root)->right = nullptr;
}
else
if (word < (*root)->data)
{
HelperInsert(&(*root)->left, word);
}
else
{
if (word > (*root)->data)
{
HelperInsert(&(*root)->right, word);
}
}
}
void HelperExists(Node *root, string word)
{
Node *temp = new Node;
temp = root;
// Run the loop untill temp points to a NULL pointer.
while(temp != NULL)
{
if(temp->data == word)
{
cout<<"True "<<endl;
}
// Shift pointer to left child.
else if(temp->data > word)
temp = temp->left;
// Shift pointer to right child.
else
temp = temp->right;
}
cout<<"\n False";
return;
}
string Helpwr(Node *root)
{
if(root == nullptr)
{
return "";
}
else
{
return inorderHelper(root->left)
+ root->data + " "
+ inorderHelper(root->right);
}
}
void HelperPreOrder(Node *root)
{
if ( root !=nullptr)
{
cout << root->data << " ";
HelperPreOrder(root->left);
HelperPreOrder(root->right);
}
}
void HelperPostorder(Node *root)
{
if (root!=nullptr)
{
HelperPostorder(root->left);
HelperPostorder(root->right);
cout << root->data<< endl;
return;
}
}
BST::BST()
{
root= nullptr;
}
// Creates a binary tree by copying an existing tree
BST::BST(const BST &rhs)
{
}
void BST::insert(string word)
{
HelperInsert(*root, word);
}
void BST::remove(string word)
{
}
bool BST::exists(string word) const
{
HelperExists(root, word);
return true;
}
std::string BST::inorder() const
{
string res = inorderHelper(root);
int len = res.length();
if(len >= 1 && res[len -1] == ' ')
{
res.pop_back();
}
return res;
}
std::string BST::preorder() const
{
HelperPreOrder(root);
return std::string("");
}
std::string BST::postorder() const
{
HelperPostorder(root);
return std::string("");
}
bool BST::operator==(const BST &other) const
{
return true;
}
bool BST::operator!=(const BST &other) const
{
return true;
}
My test file:
tree = new BinarySearchTree();
// Test 3 - insertion check
tree->insert("fish");
tree->insert("aardvark");
tree->insert("zeebra");
str = tree->inorder();
if (str != string("aardvark fish zeebra"))
cerr << "test 3 failed" << endl;
else
cout << "Test 3 passed" << endl;
// Test 4 - exists check
if (tree->exists("zeebra") && tree->exists("fish") && !tree->exists("bird") && !tree->exists("snake"))
cout << "Test 4 passed" << endl;
else
cerr << "test 4 failed" << endl;

Answer 1

Seems like an issue of not storing the string words correctly:
your insert method is as follows:
void insert(std::string word);
Which means a value of the string is passed, not a reference.
In order to store the string, you'll have to create a copy of the string and store it in memory:
string HelperInsert(Node **root, std::string word)
{
if (*root == nullptr)
{
// Create new node
*root = new Node;
// Set new value
(*root).data = new std:string(word); // note the setting of a string pointer here!
// Set branches to nullptr
(*root)->left = nullptr;
(*root)->right = nullptr;
}
else
if (word < (*root)->data)
{
HelperInsert(&(*root)->left, word);
}
else
{
if (word > (*root)->data)
{
HelperInsert(&(*root)->right, word);
}
}
}
Do not forget to delete the string when removing nodes, in order to prevent mempory leaks.
Good luck!