C++ - Creating Binary Search Tree Class, one Node disappears after rotate - c++

Question

I am trying to create a custom Binary Search Tree, and I have everything done except for the rotate function, which seems to be not moving a node over. The rotate function only gets called when a node is searched and found, and if the node has a right child. For simplicity I will only add the functions that are used in this, to make it shorter:
#include <iostream>
using namespace std;
template <typename T>
class MRBST {
public:
MRBST();
~MRBST();
void push(const T &);
bool search(const T &);
void PrintPreorder();
private:
struct Node {
T data;
Node *left;
Node *right;
Node (const T & theData, Node *lt, Node *rt)
: data(theData), left(lt), right(rt) {}
};
Node *root;
void push(const T &, Node * &) const;
void remove(const T &, Node * &) const;
Node* findMin(Node *t) const {
if (t == NULL) {
return NULL;
}
if (t->left == NULL) {
return t;
}
return findMin(t->left);
}
void preorder(Node * &);
bool search(const T &, Node *);
Node* findNode(const T & x, Node * t) {
if (t == NULL) {
return NULL;
}
if (x < t->data) {
return findNode(x, t->left);
} else if (x > t->data) {
return findNode(x, t->right);
} else if (x == t->data) {
return t;
}
return NULL;
}
void rotate(Node *);
};
template <typename T>
void MRBST<T>::PrintPreorder() {
preorder(root);
cout << endl;
}
template <typename T>
void MRBST<T>::preorder(Node * & t) {
if (t != NULL) {
cout << t->data << endl;
preorder(t->left);
preorder(t->right);
}
}
template <typename T>
bool MRBST<T>::search(const T & x) {
if (search(x, root)) {
Node *temp = findNode(x, root);
rotate(temp);
return true;
} else {
return false;
}
}
template <typename T>
void MRBST<T>::rotate(Node * k1) {
if (k1->right == NULL) {
return;
} else {
Node *temp = k1->right;
k1->right = temp->left;
temp->left = k1;
}
}
template <typename T>
bool MRBST<T>::search(const T & x, Node *t) {
if (t == NULL) {
return false;
} else if (x < t->data) {
return search(x, t->left);
} else if (x > t->data) {
return search(x, t->right);
} else {
return true;
}
}
I have a simple testing file that just adds some numbers to the tree, and then searches, followed by a print out in Preordering.
#include <iostream>
#include "MRBST.h"
using namespace std;
int main() {
MRBST<int> binaryTree;
binaryTree.push(5);
binaryTree.push(20);
binaryTree.push(3);
binaryTree.push(3);
binaryTree.push(4);
binaryTree.push(22);
binaryTree.push(17);
binaryTree.push(18);
binaryTree.push(8);
binaryTree.push(9);
binaryTree.push(1);
binaryTree.PrintPreorder();
cout << endl;
binaryTree.search(17);
binaryTree.PrintPreorder();
cout << endl;
}
With the output looking a something like this:
5
3
1
4
20
17
8
9
18
22
5
3
1
4
20
17
8
9
22
If anyone could give some insight into what is going wrong with my rotate function, that would be a great help.

Answer 1

Why are you doing rotate on search? It should be read-only.
You're losing the node because of that.
Look at your rotate:
Node *temp = k1->right;
k1->right = temp->left;
temp->left = k1;
Assume k1=x has right=y and left=z, look step by step:
Node *temp = k1->right;
temp =k1->right = y, k1 = x, k1->left = z
k1->right = temp->left;
k1->right = ?, k1->left = z, temp = y
temp->left = k1;
k1->right = ?, k1->left = z, temp->left = x.
Now - where did Y go? You lost it.

Answer 2

Look closely at your rotate() function, step by step, to see whether it does what you want it to do or not.