Accepting tree nodes from keyboard for determining it's height - c++

I have a code that can determine tree height by hard coding it's values
I tried using container like structures but still was not successful, instead of posting what I have tried on the part of accepting tree nodes fro the Input which is actually messy,I decided to post the code with hard coded tree nodes, what I need is for the program to accept tree nodes from the keyboard with the following helper description for input
Input:
The first line is an integer N indicating the number of nodes.
For each of the next few lines, there are two integers include a and b.b is a child of a.
example:
5 // number of nodes
1 2
1 3
3 4
3 5
in which the height will be 3
// C++ program to find height of tree
#include <bits/stdc++.h>
using namespace std;
/* A binary tree node has data, pointer to left child
and a pointer to right child */
class node
{
public:
int data;
node* left;
node* right;
};
/* Compute the "maxDepth" of a tree -- the number of
nodes along the longest path from the root node
down to the farthest leaf node.*/
int maxDepth(node* node)
{
if (node == NULL)
return 0;
else
{
/* compute the depth of each subtree */
int lDepth = maxDepth(node->left);
int rDepth = maxDepth(node->right);
/* use the larger one */
if (lDepth > rDepth)
return(lDepth + 1);
else return(rDepth + 1);
}
}
/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
node* newNode(int data)
{
node* Node = new node();
Node->data = data;
Node->left = NULL;
Node->right = NULL;
return(Node);
}
// Driver code
int main()
{
node *root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->left->right = newNode(5);
cout << "Height of tree is " << maxDepth(root);
return 0;
}

Since the input identifies the parent node by its data value, we need a helper function to find it:
node *findNode(node *node, int data)
{
if (!node) return 0;
if (node->data == data) return node;
class node *found;
(found = findNode(node->left, data)) || (found = findNode(node->right, data));
return found;
}
Then we can code the input processing, e. g.:
node *node, *root = 0; // initially empty
int nn, a, b;
cin>>nn;
while (cin>>a>>b)
{
if (!root)
root = newNode(a),
node = root;
else
node = findNode(root, a);
if (!node->left) node->left = newNode(b);
else node->right = newNode(b);
}

Related

How to read binary tree from file? C++

How to read file into a binary tree?
I need to read binary tree from a file then mirror it and write it out to another file. I have managed to mirror it, but can't find any way how to read it from file before mirroring. I have seen other people asking it, but none of them seem to get an answer.
#include <iostream>
using namespace std;
// Data structure to store a binary tree node
struct Node
{
int data;
Node *left, *right;
Node(int data)
{
this->data = data;
this->left = this->right = nullptr;
}
};
// Function to perform preorder traversal on a given binary tree
void preorder(Node* root)
{
if (root == nullptr) {
return;
}
cout << root->data << " ";
preorder(root->left);
preorder(root->right);
}
// Function to convert a given binary tree into its mirror
void convertToMirror(Node* root)
{
// base case: if the tree is empty
if (root == nullptr) {
return;
}
// convert left subtree
convertToMirror(root->left);
// convert right subtree
convertToMirror(root->right);
// swap left subtree with right subtree
swap(root->left, root->right);
}
int main()
{
/* Construct the following tree
1
/ \
/ \
2 3
/ \ / \
4 5 6 7
*/
Node* root = new Node(1);
root->left = new Node(2);
root->right = new Node(3);
root->left->left = new Node(4);
root->left->right = new Node(5);
root->right->left = new Node(6);
root->right->right = new Node(7);
convertToMirror(root);
preorder(root);
return 0;
}
With trees, recursive functions are usually the easiest way to go, since they allow you to iterate over the entire tree without having to manually maintain the state of the iteration.
For example, your Node::write() method (that you use to dump the state of your tree to disk) might look something like this (untested pseudocode):
void Node::write(FILE * fpOut) const
{
fprintf(fpOut, "BEGIN Node data=%i\n", data);
if (left) left->write(fpOut);
if (right) right->write(fpOut);
fprintf(fpOut, "END Node\n");
}
For example, for a tree that contains just the root (with data=1) and two children (with data=2 and data=3), that would result in a file that looks like this:
BEGIN NODE data=1
BEGIN NODE data=2
END NODE
BEGIN NODE data=3
END NODE
END NODE
... but how to read it back in? That's a bit trickier, but you can do that with a similar recursive function, something like this (again, untested pseudocode):
Node * readTree(Node * parent, FILE * fpIn)
{
char buf[128];
fgets(buf, sizeof(buf), fpIn);
while(strncmp(buf, "BEGIN NODE data=", 16) == 0)
{
Node * childNode = new Node(atoi(buf+16));
(void) readTree(childNode, fpIn); // recurse to read child node
if (parent)
{
if (parent->left == NULL) parent->left = childNode;
else if (parent->right == NULL) parent->right = childNode;
else
{
printf("File contains more than two children for node!?\n");
delete childNode; // avoid memory leak
break;
}
}
else return node; // return the root of the tree to the caller
}
return NULL;
}
Taking a page from the book of LISP, you could represent your tree as: (whitespace for clarity)
(1
(2
(4 * *)
(5 * *))
(3
(6 * *)
(7 * *)))
with a simple read function as:
Node * readTree(istream& is) {
std::istream::sentry s(is);
if (!s) {
// should not happen!
}
int data;
Node *left=nullptr, *right=nullptr;
if (is.peek() == '(') {
is.get(); // eat (
is >> data;
left = readTree(is);
right = readTree(is);
is.get(); // eat )
return TODO; // create Node from data, left, right
} else if (is.peek() == '*') {
is.get(); // eat *
return nullptr;
} else {
// should not happen!
}
}

recursive code for finding the height of a binary tree

I am trying to find the height of a binary tree and here is my attempt at the same
#include<iostream>
#include<stack>
using namespace std;
int total = 0;
int length = -1;
class Node{
public:
int data;
Node *left;
Node *right;
Node(int k){
data = k;
left = right = NULL;
}
};
void height(Node *root){
if(root==NULL)
return;
length++;
if(length>total)
total = length;
height(root->left);
height(root->right);
}
int main(){
Node *root = new Node(3);
root->left = new Node(4);
root->left->left = new Node(5);
root->right = new Node(6);
root->right->left = new Node(7);
height(root);
cout<<total;
return 0;
}
here length and total have been declared as global variables having values -1 and 0 respectively.
When I run the code, the output which I am getting is the number of nodes in the tree - 1 but not the height of the tree. Please let me know my mistake here.
Sure, you're incrementing length on every node.
If you're doing it recursively, it is actually very simple:
std::size_t height(Node const *root) {
if(!root) return 0;
return 1 + std::max(height(root->left), height(root->right));
}
Your approach is more of a backtracking than a simple recursion. In this approach you should be mindful to revert back to the original state at each step. Here length is always being incremented. You should revert it back.
void height(Node *root){
if(root==NULL)
return;
length++;
total = std::max(total,length+1); // Either this or initialize length as 0
height(root->left);
height(root->right);
length--; // <--- Add this line
}

Function to Calculate Height of Tree

I am struggling to understand how the following maxDepth function, which calculates the height of a tree, actually works.
Consider the tree:
1
/ \
2 3
/ \
4 5
\
8
In the code below, when we call the maxDepth function with the argument root, what is actually being calculated?
We declare two variables:
int lDepth = maxDepth(node->left);
int rDepth = maxDepth(node->right);
so for root we are assigning:
int lDepth = maxDepth(2);
int rDepth = maxDepth(3);
but there are no actual numeric values in here, so how do we call if (lDepth > rDepth) below this? There isn't anything to actually compare the values of is there? I would have thought the code in the if statement shouldn't execute.
#include <iostream>
using namespace std;
class node
{
public:
int data;
node* left;
node* right;
};
int maxDepth(node* node)
{
if (node == nullptr)
return 0;
else
{
/* compute the depth of each subtree */
int lDepth = maxDepth(node->left);
int rDepth = maxDepth(node->right);
/* use the larger one */
if (lDepth > rDepth)
return(lDepth+1);
else return(rDepth+1);
}
}
node* newNode(int data)
{
node* Node = new node();
Node->data = data;
Node->left = nullptr;
Node->right = nullptr;
return(Node);
}
int main()
{
node *root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->left->right = newNode(5);
root->left->right->right = newNode(8);
cout << "Height of tree is " << maxDepth(root);
return 0;
}
We declare two variables:
int lDepth = maxDepth(node->left);
int rDepth = maxDepth(node->right);
so for root we are assigning:
int lDepth = maxDepth(2);
int rDepth = maxDepth(3);
No. We are instead finding the depths of two trees
2
/ \
4 5
\
8
and
3
The maxDepth() is a recursive function. So at the second level (one level lower to the root), there are two nodes 2 and 3.
Look at node 3 first, maxDepth(3) will allocate and call itself, then check whether there's a pointer or not, sincere there's not, it will return 0 from
if (node == nullptr)
return 0;
So rDepth is 0 for the node is 3.
Similarly, for the node 2, it will do the same, with multiple self-callings and assign an integer to the lDepth.
Thinking maxDepth() as an object instead of function might help.

Inserting a node into a binary search tree in C++

I'm attempting to build a binary search tree and then do a horizontal inorder print with the left most node as the first node displayed. Also, preceding each node is its depth (distance from root) as well as a tilde to help visualize the tree itself. Conceptually my code seems to be correct, but for whatever reason I can't seem to get it to build the tree properly. I figure that the error is most likely in my insert function, but I can't seem to locate it.
Any suggestions or ideas would be extremely helpful!
#include <iostream>
#include <cstdlib>
#include <fstream>
#include <iomanip>
#include <algorithm>
using namespace std;
typedef struct treeNode {
treeNode *leftChild;
treeNode *rightChild;
int data;
} treeNode;
void printTree(treeNode*);
int getNodeDepth(treeNode*);
treeNode* insert(treeNode*, int);
treeNode* createNewNode(int);
int main()
{
//read in file here
treeNode *root = NULL;
root = insert(root, 8);
root = insert(root, 1);
root = insert(root, 90);
root = insert(root, 3);
root = insert(root, 80);
root = insert(root, 6);
root = insert(root, 83);
printTree(root);
return 0;
}
/*
Purpose: Constructs a new node for the tree.
Inputs: The data for the node.
Outputs: returns the new node
*/
treeNode* createNewNode(int data)
{
treeNode *newNode = new treeNode;
newNode->data = data;
newNode->leftChild = NULL;
newNode->rightChild = NULL;
return newNode;
}
/*
Purpose: Calculates the depth of a given node using recursion.
Inputs: The node to check the depth on.
Outputs: returns the depth
*/
int getNodeDepth(treeNode *node)
{
if (node == NULL) // tree doesn't exist
return(0);
return(1 + max(getNodeDepth(node->leftChild), getNodeDepth(node->rightChild)));
}
/*
Purpose: Inserts a node into the tree.
Inputs: The node to be inserted and the data for the node.
Outputs: returns the inserted node
*/
treeNode* insert(treeNode *node, int data)
{
if (node == NULL)
return createNewNode(data);
else
{
if (data <= node->data)
{
node->leftChild = insert(node->leftChild, data);
}
else
{
node->rightChild = insert(node->rightChild, data);
}
return node;
}
}
/*
Purpose: Prints the BST in a horizontal inorder format.
Inputs: The root node.
Outputs: nothing
*/
void printTree(treeNode *node)
{
if (node == NULL)
return;
printTree(node->leftChild);
cout << "(" << (getNodeDepth(node)-1) << ") ";
for (int i=0; i<(getNodeDepth(node)-1); i++)
cout << "~";
cout << node->data << endl;
printTree(node->rightChild);
}
The current output is as follows:
(2) ~~1
(1) ~3
(0) 6
(3) ~~~8
(1) ~80
(0) 83
(2) ~~90
Obviously it can't have two roots (ie 6 and 83). Thanks!
For those in the future who wish for a correct implementation of the answer to my original question here is the refactored code that I came up. I decided to take an OOP approach and modified the insert and getNodeDepth function to appropriately work.
//
// Binary Search Tree
//
#include <iostream>
#include <cstdlib>
#include <fstream>
#include <iomanip>
#include <algorithm>
using namespace std;
// binary search tree
class BST {
private:
typedef struct treeNode {
treeNode *leftChild;
treeNode *rightChild;
int data;
} treeNode;
treeNode *root;
public:
//Constructor
BST() { root = NULL; }
/*
Purpose: Constructs a new node for the tree.
Inputs: The data for the node.
Outputs: returns the new node
*/
treeNode* createNewNode(int data)
{
treeNode *newNode = new treeNode;
newNode->data = data;
newNode->leftChild = NULL;
newNode->rightChild = NULL;
return newNode;
}
//Check if the tree is empty
bool isEmpty() const { return root==NULL; }
/*
Purpose: Calculates the depth of a given node using recursion.
Inputs: The node to check the depth on and the node to check the depth from.
Outputs: returns the depth
*/
int getNodeDepth(treeNode *node, treeNode *from)
{
if (node == from)
return 0;
else if (node->data < from->data)
return getNodeDepth(node, from->leftChild) + 1;
else
return getNodeDepth(node, from->rightChild) + 1;
}
/*
Purpose: Inserts a node into the tree.
Inputs: The data for the node.
Outputs: none
*/
void insert(int newData)
{
treeNode* t = createNewNode(newData);
treeNode* parent;
parent = NULL;
if(isEmpty()) //check if tree exists or not
root = t;
else {
//Note: ALL insertions are as leaf nodes
treeNode* curr;
curr = root;
// Find the Node's parent
while(curr)
{
parent = curr;
if (t->data > curr->data)
curr = curr->rightChild;
else
curr = curr->leftChild;
}
if ((t->data) < (parent->data))
parent->leftChild = t;
else
parent->rightChild = t;
}
}
/*
Purpose: Prints the BST in a horizontal inorder format.
Inputs: The root node.
Outputs: nothing
*/
void printTree(treeNode *node)
{
if (node == NULL)
return;
printTree(node->leftChild);
cout << "(" << getNodeDepth(node, root) << ") ";
for (int i=0; i<getNodeDepth(node, root); i++)
cout << "~";
cout << node->data << endl;
printTree(node->rightChild);
}
//Getter for private member variable root
void printInorder()
{
printTree(root);
}
};
int main()
{
// read file in here
BST temp;
temp.insert(8);
temp.insert(1);
temp.insert(90);
temp.insert(3);
temp.insert(80);
temp.insert(6);
temp.insert(83);
temp.printInorder();
return 0;
}
The correct output looks as follows with 8 as the root:
(1) ~1
(2) ~~3
(3) ~~~6
(0) 8
(2) ~~80
(3) ~~~83
(1) ~90
Hope this helps!
In the first you shouldn't write treeNode twice
typedef struct {
treeNode *leftChild;
treeNode *rightChild;
int data;
} treeNode;
In the second you create a memory leak:
treeNode *root = new treeNode;
root = NULL;
You should write:
treeNode *root = NULL;
Obviously it can't have two roots (ie 6 and 83). Thanks!
6 and 83 aren't roots. 8 is a root. So your program gave right answer.

Build a binary tree from a given preorder traversal

I have a preorder traversal of a binary tree that is stored in an array and I would like to recreate the binary tree based on this traversal. My array looks like this: {NNNLLNLLNLNLNNLLNLL}, where N represents a node and L represents a leaf. I would like to do this recursively but I am having trouble coming up with an algorithm. Any suggestions would be very appreciated.
This should work assuming every node has 2 or 0 descendants (a tree that satisfies this property is called full or strict binary tree)
void create_from_traversal(Node* root, int& index) {
if (traversal[index] == 'L') {
root->left = root->right = NULL;
return;
}
root->left = new Node();
create_from_traversal(root->left, ++index);
root->right = new Node();
create_from_traversal(root->right, ++index);
}
Complete example with check:
#include <string>
#include <iostream>
class Node {
public:
Node* left;
Node* right;
};
std::string traversal = "NNNLLNLLNLNLNNLLNLL";
void create_from_traversal(Node* root, int& index) {
if (traversal[index] == 'L') {
root->left = root->right = NULL;
return;
}
root->left = new Node();
create_from_traversal(root->left, ++index);
root->right = new Node();
create_from_traversal(root->right, ++index);
}
void print_traversal(Node* root) {
if (root->left == NULL) {
std::cout << "L";
return;
}
std::cout << "N";
print_traversal(root->left);
print_traversal(root->right);
}
int main() {
Node* root = new Node();
int index = 0;
create_from_traversal(root, index);
// Does it work?
print_traversal(root); // Output should be equal to given traversal
std::cout << std::endl;
}
Output:
NNNLLNLLNLNLNNLLNLL
You need one more traversal before you can reconstruct the tree. Given any two traversals among the three (Pre, Post, In) you can reconstruct. But given only one it is not possible to uniquely reconstruct the tree.