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Combining two binary trees into one

Heiru (7)
Hello again. I need to write a function that combines two binary trees that entered by the user into a new binary tree.
I have the general program down but i have literally no idea how to write the function that i need. Can somebody help with that? 

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#include <iostream>

using namespace std;

struct tree
{
	char key;
	tree* left;
	tree* right;
}*root=NULL;

void add(int n, tree* t);
void preorder(tree* t);
int del(int k);
tree*& search(int k);
tree* search_iter(tree* t, int k);
int height(tree* t);
void print_node(int n, int h);
void show(tree* t, int h);

int main()
{
	int num, choice = 0, h;

	do
	{
		cout << "\t\tMenu" << endl;
		cout << "1. Add element to binary tree" << endl;
		cout << "2. Print" << endl;
		cout << "3. Search element in binary tree" << endl;
		cout << "4. Delete element" << endl;
		cout << "5. Show" << endl;
		cout << "6. Exit" << endl;
		cout << "Enter your choice: " << endl;
		cin >> choice;

		switch (choice)
		{
		case 1:
			cout << "num=";
			cin >> num;
			add(num, root);
			break;
		case 2:
			cout << "All elements" << endl;
			preorder(root);
			break;
		case 3:
			cout << "Search: ";
			cin >> num;
			tree*& p = search(num);
			if (p == NULL)
				cout << "The element is NOT in the tree\n";
			else
				cout << "The element is in the tree\n";
			break;
		case 4:
			cout << "Enter element to delete: ";
			cin >> num;
			if (del(num) == 0)
				cout << "The element is NOT in the tree\n";
			break;
		case 5:
			h = height(root);
			show(root, h);
			cout << "\n";
			break;
		case 6:
			exit(0);
			break;
		}
	}while (choice != 6);
	system("pause");

	return 0;
}

void add(int n, tree* t)
{
	if (t == NULL)
	{
		t = new tree;
		t->key = n;
		t->left = t->right = NULL;
	}
	else
	{
		if (t->key < n)
			add(n, t->right);
		else
			add(n, t->left);
	}
}

void preorder(tree* t)
{
	if (t)
	{
		cout << t->key << " ";
		preorder(t->left);
		preorder(t->right);
	}
}

int del(int k)
{
	tree*& p = search(k), * p0 = p, ** qq, * q;
	if (p == NULL)
		return 0;

	if (p->right == NULL)
	{
		p = p->left;
		delete p0;
	}
	else
		if (p->left == NULL)
		{
			p = p->right;
			delete p0;
		}
		else
		{
			qq = &p->left;
			while ((*qq)->right)
				qq = &(*qq)->right;
			p->key = (*qq)->key;
			q = *qq;
			*qq = q->left;
			delete q;
		}
	return 1;
}

tree*& search(int k)
{
	tree** p = &root;

	for (;;)
	{
		if (*p == NULL)
			return *p;
		if (k < (*p)->key)
			p = &(*p)->left;
		else
			if (k > (*p)->key)
				p = &(*p)->right;
			else
				return *p;
	}
}

tree* search_iter(tree* t, int k)
{
	while (t && t->key != k)
		if (t->key < k)
			t = t->right;
		else
			t = t->left;

	return t;
}

int height(tree* t)
{
	int u, v;

	if (!t)
		return -1;
	u = height(t->left);
	v = height(t->right);

	if (u > v)
		return u + 1;
	else
		return v + 1;
}

void print_node(int n, int h)
{
	for (int i = 0; i < h; i++)
		cout << "\t";
	cout << n << "\n";
}

void show(tree* t, int h)
{
	if (t)
	{
		show(t->right, h + 1);
		print_node(t->key, h);
		show(t->left, h + 1);
	}
}
AbstractionAnon (6954)
Line 83: You have a type mismatch. You're passing in an int, but trying to store it in a char.

As to your question, show() shows you can walk the tree. To merge two trees, simply walk one tree and add each element to to the other tree.
jonnin (11329)
If you have a binary SEARCH tree (it appears that you DO), you have to insert each node (I don't know of any shortcuts). If it is just a binary tree, you can stuff the root of one tree in as a child on any open (null) pointer leaf node, intact, a single pointer assignment and its done.
Last edited on
seeplus (6456)
Small point. But in C++ it's nullptr instead of NULL (which is c) for null pointers.

seeplus (6456)
Also there is a problem with add. It doesn't update root if first add. Perhaps:

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#include <iostream>

struct tree {
	int key {};
	tree* left {};
	tree* right {};

	tree(int k) : key(k) {}
};

tree *root {};

void add(int n, tree*& t);
void preorder(tree* t);
bool del(int k);
tree*& search(int k);
tree* search_iter(tree* t, int k);
int height(tree* t);
void print_node(int n, int h);
void show(tree* t, int h);

int main() {
	int num {}, choice {};

	do {
		std::cout << "\t\tMenu\n" <<
			"1. Add element to binary tree\n" <<
			"2. Print\n"  <<
			"3. Search element in binary tree\n" <<
			"4. Delete element\n" <<
			"5. Show\n" <<
			"6. Exit\n" <<
			"\nEnter your choice: ";

		std::cin >> choice;

		switch (choice) {
		case 1: {
			auto temp { root };

			std::cout << "num= ";
			std::cin >> num;
			add(num, temp);

			if (!root)
				root = temp;
		}
			break;

		case 2:
			std::cout << "All elements\n";
			preorder(root);
			std::cout << '\n';
			break;

		case 3: {
			std::cout << "Search: ";
			std::cin >> num;
			tree*& p = search(num);
			if (!p)
				std::cout << "The element is NOT in the tree\n";
			else
				std::cout << "The element is in the tree\n";
		}
			break;

		case 4:
			std::cout << "Enter element to delete: ";
			std::cin >> num;
			if (!del(num))
				std::cout << "The element is NOT in the tree\n";

			break;

		case 5:
			show(root, height(root));
			std::cout << '\n';
			break;

		case 6:
			//exit(0);
			break;

		default:
			std::cout << "Invalid option\n";
			break;
		}
	} while (choice != 6);
}

void add(int n, tree* &t) {
	if (!t)
		t = new tree(n);
	else
		add(n, t->key < n ? t->right : t->left);
}

void preorder(tree* t) {
	if (t) {
		std::cout << t->key << ' ';
		preorder(t->left);
		preorder(t->right);
	}
}

bool del(int k) {
	tree* &p { search(k) }, *p0 { p };

	if (!p)
		return false;

	if (!p->right) {
		p = p->left;
		delete p0;
	} else if (!p->left) {
			p = p->right;
			delete p0;
		} else {
		    auto qq { &p->left };

			while ((*qq)->right)
				qq = &(*qq)->right;

			p->key = (*qq)->key;

			auto q { *qq };

			*qq = q->left;
			delete q;
		}

	return true;
}

tree*& search(int k) {
	tree** p { &root };

	for (;;) {
		if (*p == nullptr)
			return *p;

		if (k < (*p)->key)
			p = &(*p)->left;
		else
			if (k > (*p)->key)
				p = &(*p)->right;
			else
				return *p;
	}
}

tree* search_iter(tree* t, int k) {
	while (t && t->key != k)
		t = t->key < k ? t->right : t->left;

	return t;
}

int height(tree* t) {
	if (!t)
		return -1;

	auto u { height(t->left) };
	auto v { height(t->right) };

	return 1 + (u > v ? u : v);
}

void print_node(int n, int h) {
	for (int i {}; i < h; ++i)
		std::cout << '\t';

	std::cout << n << '\n';
}

void show(tree* t, int h) {
	if (t) {
		show(t->right, h + 1);
		print_node(t->key, h);
		show(t->left, h + 1);
	}
}

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