Print a binary tree in a pretty way
Just wondering if I can get some tips on printing a pretty binary tree in the form of:
5
10
11
7
6
3
4
2
Right now what it prints is:
2
4
3
6
7
11
10
5
I know that my example is upside down from what I'm currently printing, which it doesn't matter if I print from the root down as it currently prints. Any tips are very appreciated towards my full question:
How do I modify my prints to make the tree look like a tree?
//Binary Search Tree Program
#include <iostream>
#include <cstdlib>
#include <queue>
using namespace std;
int i = 0;
class BinarySearchTree
{
private:
struct tree_node
{
tree_node* left;
tree_node* right;
int data;
};
tree_node* root;
public:
BinarySearchTree()
{
root = NULL;
}
bool isEmpty() const { return root==NULL; }
void print_inorder();
void inorder(tree_node*);
void print_preorder();
void preorder(tree_node*);
void print_postorder();
void postorder(tree_node*);
void insert(int);
void remove(int);
};
// Smaller elements go left
// larger elements go right
void BinarySearchTree::insert(int d)
{
tree_node* t = new tree_node;
tree_node* parent;
t->data = d;
t->left = NULL;
t->right = NULL;
parent = NULL;
// is this a new tree?
if(isEmpty()) root = t;
else
{
//Note: ALL insertions are as leaf nodes
tree_node* curr;
curr = root;
// Find the Node's parent
while(curr)
{
parent = curr;
if(t->data > curr->data) curr = curr->right;
else curr = curr->left;
}
if(t->data < parent->data)
{
parent->left = t;
}
else
{
parent->right = t;
}
}
}
void BinarySearchTree::remove(int d)
{
//Locate the element
bool found = false;
if(isEmpty())
{
cout<<" This Tree is empty! "<<endl;
return;
}
tree_node* curr;
tree_node* parent;
curr = root;
while(curr != NULL)
{
if(curr->data == d)
{
found = true;
break;
}
else
{
parent = curr;
if(d>curr->data) curr = curr->right;
else curr = curr->left;
}
}
if(!found)
{
cout<<" Data not found! "<<endl;
return;
}
// 3 cases :
// 1. We're removing a leaf node
// 2. We're removing a node with a single child
// 3. we're removing a node with 2 children
// Node with single child
if((curr->left == NULL && curr->right != NULL) || (curr->left != NULL && curr->right == NULL))
{
if(curr->left == NULL && curr->right != NULL)
{
if(parent->left == curr)
{
parent->left = curr->right;
delete curr;
}
else
{
parent->right = curr->left;
delete curr;
}
}
return;
}
//We're looking at a leaf node
if( curr->left == NULL && curr->right == NULL)
{
if(parent->left == curr)
{
parent->left = NULL;
}
else
{
parent->right = NULL;
}
delete curr;
return;
}
//Node with 2 children
// replace node with smallest value in right subtree
if (curr->left != NULL && curr->right != NULL)
{
tree_node* chkr;
chkr = curr->right;
if((chkr->left == NULL) && (chkr->right == NULL))
{
curr = chkr;
delete chkr;
curr->right = NULL;
}
else // right child has children
{
//if the node's right child has a left child
// Move all the way down left to locate smallest element
if((curr->right)->left != NULL)
{
tree_node* lcurr;
tree_node* lcurrp;
lcurrp = curr->right;
lcurr = (curr->right)->left;
while(lcurr->left != NULL)
{
lcurrp = lcurr;
lcurr = lcurr->left;
}
curr->data = lcurr->data;
delete lcurr;
lcurrp->left = NULL;
}
else
{
tree_node* tmp;
tmp = curr->right;
curr->data = tmp->data;
curr->right = tmp->right;
delete tmp;
}
}
return;
}
}
void BinarySearchTree::print_postorder()
{
postorder(root);
}
void BinarySearchTree::postorder(tree_node* p)
{
if(p != NULL)
{
if(p->left) postorder(p->left);
if(p->right) postorder(p->right);
cout<<" "<<p->data<<"\n ";
}
else return;
}
int main()
{
BinarySearchTree b;
int ch,tmp,tmp1;
while(1)
{
cout<<endl<<endl;
cout<<" Binary Search Tree Operations "<<endl;
cout<<" ----------------------------- "<<endl;
cout<<" 1. Insertion/Creation "<<endl;
cout<<" 2. Printing "<<endl;
cout<<" 3. Removal "<<endl;
cout<<" 4. Exit "<<endl;
cout<<" Enter your choice : ";
cin>>ch;
switch(ch)
{
case 1 : cout<<" Enter Number to be inserted : ";
cin>>tmp;
b.insert(tmp);
i++;
break;
case 2 : cout<<endl;
cout<<" Printing "<<endl;
cout<<" --------------------"<<endl;
b.print_postorder();
break;
case 3 : cout<<" Enter data to be deleted : ";
cin>>tmp1;
b.remove(tmp1);
break;
case 4:
return 0;
}
}
}
Solution 1:
In order to pretty-print a tree recursively, you need to pass two arguments to your printing function:
- The tree node to be printed, and
- The indentation level
For example, you can do this:
void BinarySearchTree::postorder(tree_node* p, int indent=0)
{
if(p != NULL) {
if(p->left) postorder(p->left, indent+4);
if(p->right) postorder(p->right, indent+4);
if (indent) {
std::cout << std::setw(indent) << ' ';
}
cout<< p->data << "\n ";
}
}
The initial call should be postorder(root);
If you would like to print the tree with the root at the top, move cout to the top of the if.
Solution 2:
void btree::postorder(node* p, int indent)
{
if(p != NULL) {
if(p->right) {
postorder(p->right, indent+4);
}
if (indent) {
std::cout << std::setw(indent) << ' ';
}
if (p->right) std::cout<<" /\n" << std::setw(indent) << ' ';
std::cout<< p->key_value << "\n ";
if(p->left) {
std::cout << std::setw(indent) << ' ' <<" \\\n";
postorder(p->left, indent+4);
}
}
}
With this tree:
btree *mytree = new btree();
mytree->insert(2);
mytree->insert(1);
mytree->insert(3);
mytree->insert(7);
mytree->insert(10);
mytree->insert(2);
mytree->insert(5);
mytree->insert(8);
mytree->insert(6);
mytree->insert(4);
mytree->postorder(mytree->root);
Would lead to this result:
