Replace node with depth in a binary tree

Given a binary tree, replace each node with its depth value. For example, consider the following tree. Root is at depth 0, change its value to 0 and next level nodes are at depth 1 and so on. 

       3                       0
      /  \                    /   \
     2    5      == >;         1     1
   /   \                   /   \
  1     4                 2     2

The idea is to traverse tree starting from root. While traversing pass depth of node as parameter. We can track depth by passing it as 0 for root and one-plus-current-depth for children.

Below is the implementation of the idea. 

C++

// CPP program to replace every key value
// with its depth.
#include<bits/stdc++.h>
using namespace std;

/* A tree node structure */
struct Node
{
    int data;
    struct Node *left, *right;
};

/* Utility function to create a
   new Binary Tree node */
struct Node* newNode(int data)
{
    Node *temp = new Node;
    temp->data = data;
    temp->left = temp->right = NULL;
    return temp;
}

// Helper function replaces the data with depth
// Note : Default value of level is 0 for root.
void replaceNode(struct Node *node, int level=0)
{
    // Base Case
    if (node == NULL)
        return;

    // Replace data with current depth
    node->data = level;

    replaceNode(node->left, level+1);
    replaceNode(node->right, level+1);
}

// A utility function to print inorder
// traversal of a Binary Tree
void printInorder(struct Node* node)
{
     if (node == NULL)
          return;
     printInorder(node->left);
     cout << node->data <<" ";
     printInorder(node->right);
}

/* Driver function to test above functions */
int main()
{
    struct Node *root = new struct Node;

    /* Constructing tree given in
       the above figure */
    root = newNode(3);
    root->left = newNode(2);
    root->right = newNode(5);
    root->left->left = newNode(1);
    root->left->right = newNode(4);

    cout << "Before Replacing Nodes\n";
    printInorder(root);
    replaceNode(root);
    cout << endl;

    cout << "After Replacing Nodes\n";
    printInorder(root);

    return 0;
}

Java

// Java program to replace every key value
// with its depth.
class GfG {

/* A tree node structure */
static class Node
{
    int data;
    Node left, right;
}

/* Utility function to create a
new Binary Tree node */
static Node newNode(int data)
{
    Node temp = new Node();
    temp.data = data;
    temp.left = null;
    temp.right = null;
    return temp;
}

// Helper function replaces the data with depth
// Note : Default value of level is 0 for root.
static void replaceNode(Node node, int level)
{
    // Base Case
    if (node == null)
        return;

    // Replace data with current depth
    node.data = level;

    replaceNode(node.left, level+1);
    replaceNode(node.right, level+1);
}

// A utility function to print inorder
// traversal of a Binary Tree
static void printInorder(Node node)
{
    if (node == null)
        return;
    printInorder(node.left);
    System.out.print(node.data + " ");
    printInorder(node.right);
}

/* Driver function to test above functions */
public static void main(String[] args)
{
    Node root = new Node();

    /* Constructing tree given in
    the above figure */
    root = newNode(3);
    root.left = newNode(2);
    root.right = newNode(5);
    root.left.left = newNode(1);
    root.left.right = newNode(4);

    System.out.println("Before Replacing Nodes");
    printInorder(root);
    replaceNode(root, 0);
    System.out.println();

    System.out.println("After Replacing Nodes");
    printInorder(root);

}
}

Python3

# Python3 program to replace every key
# value with its depth.

class newNode:
    def __init__(self, data):
        self.data = data
        self.left = self.right = None

# Helper function replaces the data with depth
# Note : Default value of level is 0 for root.
def replaceNode(node, level = 0):

    # Base Case
    if (node == None):
        return

    # Replace data with current depth
    node.data = level

    replaceNode(node.left, level + 1)
    replaceNode(node.right, level + 1)

# A utility function to print inorder
# traversal of a Binary Tree
def printInorder(node):
    if (node == None):
        return
    printInorder(node.left)
    print(node.data, end = " ")
    printInorder(node.right)

# Driver Code
if __name__ == '__main__':

    # Constructing tree given in
    # the above figure
    root = newNode(3)
    root.left = newNode(2)
    root.right = newNode(5)
    root.left.left = newNode(1)
    root.left.right = newNode(4)

    print("Before Replacing Nodes")
    printInorder(root)
    replaceNode(root)

    print()
    print("After Replacing Nodes")
    printInorder(root)

# This code is contributed by PranchalK

C#

// C# program to replace every key value
// with its depth.
using System;

public class GfG
{

    /* A tree node structure */
    public class Node
    {
        public int data;
        public Node left, right;
    }

    /* Utility function to create a
    new Binary Tree node */
    static Node newNode(int data)
    {
        Node temp = new Node();
        temp.data = data;
        temp.left = null;
        temp.right = null;
        return temp;
    }

    // Helper function replaces the data with depth
    // Note : Default value of level is 0 for root.
    static void replaceNode(Node node, int level)
    {
        // Base Case
        if (node == null)
            return;

        // Replace data with current depth
        node.data = level;

        replaceNode(node.left, level + 1);
        replaceNode(node.right, level + 1);
    }

    // A utility function to print inorder
    // traversal of a Binary Tree
    static void printInorder(Node node)
    {
        if (node == null)
            return;
        printInorder(node.left);
        Console.Write(node.data + " ");
        printInorder(node.right);
    }

    /* Driver code*/
    public static void Main(String[] args)
    {
        Node root = new Node();

        /* Constructing tree given in
        the above figure */
        root = newNode(3);
        root.left = newNode(2);
        root.right = newNode(5);
        root.left.left = newNode(1);
        root.left.right = newNode(4);

        Console.WriteLine("Before Replacing Nodes");
        printInorder(root);
        replaceNode(root, 0);
        Console.WriteLine();

        Console.WriteLine("After Replacing Nodes");
        printInorder(root);
    }
}

// This code is contributed Rajput-Ji

Javascript

<script>

    // JavaScript program to replace every
    // key value with its depth.

    class Node
    {
        constructor(data) {
           this.left = null;
           this.right = null;
           this.data = data;
        }
    }

    /* Utility function to create a
    new Binary Tree node */
    function newNode(data)
    {
        let temp = new Node(data);
        return temp;
    }

    // Helper function replaces the data with depth
    // Note : Default value of level is 0 for root.
    function replaceNode(node, level)
    {
        // Base Case
        if (node == null)
            return;

        // Replace data with current depth
        node.data = level;

        replaceNode(node.left, level+1);
        replaceNode(node.right, level+1);
    }

    // A utility function to print inorder
    // traversal of a Binary Tree
    function printInorder(node)
    {
        if (node == null)
            return;
        printInorder(node.left);
        document.write(node.data + " ");
        printInorder(node.right);
    }

    let root = new Node();

    /* Constructing tree given in
    the above figure */
    root = newNode(3);
    root.left = newNode(2);
    root.right = newNode(5);
    root.left.left = newNode(1);
    root.left.right = newNode(4);

    document.write("Before Replacing Nodes" + "</br>");
    printInorder(root);
    replaceNode(root, 0);
    document.write("</br>");
    document.write("</br>");

    document.write("After Replacing Nodes" + "</br>");
    printInorder(root);

</script>

Output

Before Replacing Nodes
1 2 4 3 5 
After Replacing Nodes
2 1 2 0 1 

Time Complexity: O(n) 
Space Complexity: If we don’t consider size of stack for function calls then O(1) otherwise O(h)

Iterative Approach(Using Queue data structure):
Follow the below steps to solve the above problem:
1) Perform level order traversal with the help of queue data structure.
2) At each level keep track to level(indexing 0) and replace all nodes data of current level to level value.
3) Print the Inorder traversal of resultant tree.
Below is the implementation of above approach:

C++

// C++ Program to replace every node data
// with its depth
#include<bits/stdc++.h>
using namespace std;

// a tree node
struct Node{
    int data;
    struct Node *left, *right;
};

// utility function to create a new node
struct Node* newNode(int data){
    Node* temp = new Node();
    temp->data = data;
    temp->left = temp->right = NULL;
    return temp;
}

// Helper function replaces the data with depth
// Note : Default value of level is 0 for root.
void replaceNode(struct Node* root){
    // base case
    if(root == NULL) return;

    queue<Node*> q;
    int level = 0;
    q.push(root);
    while(!q.empty()){
        int n = q.size();
        for(int i = 0; i<n; i++){
            Node* front_node = q.front();
            q.pop();
            front_node->data = level;
            if(front_node->left) q.push(front_node->left);
            if(front_node->right) q.push(front_node->right);
        }
        level++;
    }
}

// A utility function to print inorder
// traversal of a Binary Tree
void printInorder(struct Node* node){
     if (node == NULL)
          return;
     printInorder(node->left);
     cout << node->data <<" ";
     printInorder(node->right);
}

// Driver function to test above functions
int main(){
    struct Node *root = new struct Node;
    root = newNode(3);
    root->left = newNode(2);
    root->right = newNode(5);
    root->left->left = newNode(1);
    root->left->right = newNode(4);

    cout << "Before Replacing Nodes\n";
    printInorder(root);

    replaceNode(root);
    cout << endl;

    cout << "After Replacing Nodes\n";
    printInorder(root);

    return 0;
}
// THIS CODE IS CONTRIBUTED BY YASH AGARWAL(YASHAGARWAL2852002)

Java

// Java Program to replace every node data with its depth

import java.io.*;
import java.util.*;

class Node {
    int data;
    Node left, right;
}

class GFG {

    // utility function to create a new node
    static Node newNode(int data)
    {
        Node temp = new Node();
        temp.data = data;
        temp.left = temp.right = null;
        return temp;
    }

    // Helper function replaces the data with depth
    // Note : Default value of level is 0 for root.
    static void replaceNode(Node root)
    {
        // base case
        if (root == null)
            return;

        Queue<Node> q = new LinkedList<>();
        int level = 0;
        q.add(root);
        while (!q.isEmpty()) {
            int n = q.size();
            for (int i = 0; i < n; i++) {
                Node frontNode = q.poll();
                frontNode.data = level;
                if (frontNode.left != null)
                    q.add(frontNode.left);
                if (frontNode.right != null)
                    q.add(frontNode.right);
            }
            level++;
        }
    }

    // A utility function to print inorder traversal of a
    // Binary Tree
    static void printInorder(Node node)
    {
        if (node == null)
            return;
        printInorder(node.left);
        System.out.print(node.data + " ");
        printInorder(node.right);
    }

    public static void main(String[] args)
    {
        Node root = newNode(3);
        root.left = newNode(2);
        root.right = newNode(5);
        root.left.left = newNode(1);
        root.left.right = newNode(4);

        System.out.println("Before Replacing Nodes");
        printInorder(root);

        replaceNode(root);
        System.out.println();

        System.out.println("After Replacing Nodes");
        printInorder(root);
    }
}

// This code is contributed by karthik.

Python3

# Python program to replace every node data
# with its depth

# a tree node


class Node:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None

# Helper function replaces the data with depth
# Note : Default value of level is 0 for root.


def replaceNode(root):
    # base case
    if root is None:
        return

    queue = []
    level = 0
    queue.append(root)

    while queue:
        n = len(queue)
        for i in range(n):
            front_node = queue.pop(0)
            front_node.data = level
            if front_node.left:
                queue.append(front_node.left)
            if front_node.right:
                queue.append(front_node.right)
        level += 1

# A utility function to print inorder
# traversal of a Binary Tree


def printInorder(node):
    if node is None:
        return
    printInorder(node.left)
    print(node.data, end=" ")
    printInorder(node.right)


# Driver function to test above functions
if __name__ == '__main__':
    root = Node(3)
    root.left = Node(2)
    root.right = Node(5)
    root.left.left = Node(1)
    root.left.right = Node(4)

    print("Before Replacing Nodes")
    printInorder(root)

    replaceNode(root)
    print()

    print("After Replacing Nodes")
    printInorder(root)

C#

// C# Program to replace every node data with its depth

using System;
using System.Collections.Generic;

class Node {
    public int data;
    public Node left, right;
}

public class GFG {

    // utility function to create a new node
    static Node newNode(int data)
    {
        Node temp = new Node();
        temp.data = data;
        temp.left = temp.right = null;
        return temp;
    }

    // Helper function replaces the data with depth Note :
    // Default value of level is 0 for root.
    static void replaceNode(Node root)
    {
        // base case
        if (root == null)
            return;

        Queue<Node> q = new Queue<Node>();
        int level = 0;
        q.Enqueue(root);
        while (q.Count > 0) {
            int n = q.Count;
            for (int i = 0; i < n; i++) {
                Node frontNode = q.Dequeue();
                frontNode.data = level;
                if (frontNode.left != null)
                    q.Enqueue(frontNode.left);
                if (frontNode.right != null)
                    q.Enqueue(frontNode.right);
            }
            level++;
        }
    }

    // A utility function to print inorder traversal of a
    // Binary Tree
    static void printInorder(Node node)
    {
        if (node == null)
            return;
        printInorder(node.left);
        Console.Write(node.data + " ");
        printInorder(node.right);
    }

    static public void Main()
    {

        // Code
        Node root = newNode(3);
        root.left = newNode(2);
        root.right = newNode(5);
        root.left.left = newNode(1);
        root.left.right = newNode(4);

        Console.WriteLine("Before Replacing Nodes");
        printInorder(root);

        replaceNode(root);
        Console.WriteLine();

        Console.WriteLine("After Replacing Nodes");
        printInorder(root);
    }
}

// This code is contributed by sankar.

Javascript

// JavaScript program to replace every node data
// with its depth

// a trree node
class Node{
    constructor(data){
        this.data = data;
        this.left = this.right = null;
    }
}

// utility function to create a new node
function newNode(data){
    return new Node(data);
}

// Helper function replaces the data with depth
// Note : Default value of level is 0 for root.
function replaceNode(root){
    // base case
    if(root == null) return;

    let q = [];
    let level = 0;
    q.push(root);
    while(q.length > 0){
        let n = q.length;
        for(let i = 0; i<n; i++){
            let front_node = q.shift();
            front_node.data = level;
            if(front_node.left) q.push(front_node.left);
            if(front_node.right) q.push(front_node.right);
        }
        level++;
    }
}

// A utility function to print inorder
// traversal of a Binary Tree
function printInorder(node){
    if(node == null) return;
    printInorder(node.left);
    console.log(node.data + " ");
    printInorder(node.right);
}

// driver function to test above functions
let root = newNode(3);
root.left = newNode(2);
root.right = newNode(5);
root.left.left = newNode(1);
root.left.right = newNode(4);

console.log("Before replacing Nodes : ");
printInorder(root);

replaceNode(root);

console.log("After replacing Nodes : ");
printInorder(root);

Output

Before Replacing Nodes
1 2 4 3 5 
After Replacing Nodes
2 1 2 0 1 

Time Complexity: O(N) where N is the number of nodes in given binary tree
Auxiliary Space: O(N) due to queue data structure