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Find next right node of a given key | Set 2

  • Difficulty Level : Medium
  • Last Updated : 30 Jun, 2021

Given a Binary tree and a key in the binary tree, find the node right to the given key. If there is no node on right side, then return NULL. Expected time complexity is O(n) where n is the number of nodes in the given binary tree.
For example, consider the following Binary Tree. Output for 2 is 6, output for 4 is 5. Output for 10, 6 and 5 is NULL. 

                  10
               /      \
             2         6
           /   \         \ 
         8      4          5
Input : 2
Output : 6

Input : 4
Output : 5

In our previous post we have discussed about a solution using Level Order Traversal. In this post we will discuss about a solution based on Preorder traversal which takes constant auxiliary space.
The idea is to traverse the given tree using preorder traversal and search for the given key. Once we found the given key, we will mark the level number for this key. Now the next node we will find at the same level is the required node which is at the right of given key.
Below is the implementation of above idea: 

C++




/* C++ program to find next right of a given key
   using preorder traversal */
#include <bits/stdc++.h>
using namespace std;
 
// A Binary Tree Node
struct Node {
    struct Node *left, *right;
    int key;
};
 
// Utility function to create a new tree node
Node* newNode(int key)
{
    Node* temp = new Node;
    temp->key = key;
    temp->left = temp->right = NULL;
    return temp;
}
 
// Function to find next node for given node
// in same level in a binary tree by using
// pre-order traversal
Node* nextRightNode(Node* root, int k, int level,
                               int& value_level)
{
    // return null if tree is empty
    if (root == NULL)
        return NULL;
 
    // if desired node is found, set value_level
    // to current level
    if (root->key == k) {
        value_level = level;
        return NULL;
    }
 
    // if value_level is already set, then current
    // node is the next right node
    else if (value_level) {
        if (level == value_level)
            return root;
    }
 
    // recurse for left subtree by increasing level by 1
    Node* leftNode = nextRightNode(root->left, k,
                        level + 1,  value_level);
 
    // if node is found in left subtree, return it
    if (leftNode)
        return leftNode;
 
    // recurse for right subtree by increasing level by 1
    return nextRightNode(root->right, k, level + 1,
                                       value_level);
}
 
// Function to find next node of given node in the
//  same level in given binary tree
Node* nextRightNodeUtil(Node* root, int k)
{
    int value_level = 0;
 
    return nextRightNode(root, k, 1, value_level);
}
 
// A utility function to test above functions
void test(Node* root, int k)
{
    Node* nr = nextRightNodeUtil(root, k);
    if (nr != NULL)
        cout << "Next Right of " << k << " is "
             << nr->key << endl;
    else
        cout << "No next right node found for "
             << k << endl;
}
 
// Driver program to test above functions
int main()
{
    // Let us create binary tree given in the
    // above example
    Node* root = newNode(10);
    root->left = newNode(2);
    root->right = newNode(6);
    root->right->right = newNode(5);
    root->left->left = newNode(8);
    root->left->right = newNode(4);
 
    test(root, 10);
    test(root, 2);
    test(root, 6);
    test(root, 5);
    test(root, 8);
    test(root, 4);
    return 0;
}

Java




/* Java program to find next right of a given key
using preorder traversal */
import java.util.*;
class GfG {
     
// A Binary Tree Node
static class Node {
    Node left, right;
    int key;
}
 
// Utility function to create a new tree node
static Node newNode(int key)
{
    Node temp = new Node();
    temp.key = key;
    temp.left = null;
    temp.right = null;
    return temp;
}
 
// Function to find next node for given node
// in same level in a binary tree by using
// pre-order traversal
static Node nextRightNode(Node root, int k, int level, int[] value)
{
    // return null if tree is empty
    if (root == null)
        return null;
 
    // if desired node is found, set value[0]
    // to current level
    if (root.key == k) {
        value[0] = level;
        return null;
    }
 
    // if value[0] is already set, then current
    // node is the next right node
    else if (value[0] != 0) {
        if (level == value[0])
            return root;
    }
 
    // recurse for left subtree by increasing level by 1
    Node leftNode = nextRightNode(root.left, k, level + 1, value);
 
    // if node is found in left subtree, return it
    if (leftNode != null)
        return leftNode;
 
    // recurse for right subtree by increasing level by 1
    return nextRightNode(root.right, k, level + 1, value);
}
 
// Function to find next node of given node in the
// same level in given binary tree
static Node nextRightNodeUtil(Node root, int k)
{
     
    int[] v = new int[1];
    v[0] = 0;
    return nextRightNode(root, k, 1, v);
}
 
// A utility function to test above functions
static void test(Node root, int k)
{
    Node nr = nextRightNodeUtil(root, k);
    if (nr != null)
        System.out.println("Next Right of " + k + " is "+ nr.key);
    else
        System.out.println("No next right node found for " + k);
}
 
// Driver program to test above functions
public static void main(String[] args)
{
    // Let us create binary tree given in the
    // above example
    Node root = newNode(10);
    root.left = newNode(2);
    root.right = newNode(6);
    root.right.right = newNode(5);
    root.left.left = newNode(8);
    root.left.right = newNode(4);
 
    test(root, 10);
    test(root, 2);
    test(root, 6);
    test(root, 5);
    test(root, 8);
    test(root, 4);
}
}
// This code has been contributed by Mukul Sharma

Python3




# Python3 program to find next right of a
# given key using preorder traversal
 
# class to create a new tree node
class newNode:
    def __init__(self, key):
        self.key = key
        self.left = self.right = None
 
# Function to find next node for given node
# in same level in a binary tree by using
# pre-order traversal
def nextRightNode(root, k, level, value_level):
     
    # return None if tree is empty
    if (root == None):
        return None
 
    # if desired node is found, set
    # value_level to current level
    if (root.key == k):
        value_level[0] = level
        return None
 
    # if value_level is already set, then
    # current node is the next right node
    elif (value_level[0]):
        if (level == value_level[0]):
            return root
 
    # recurse for left subtree by increasing
    # level by 1
    leftNode = nextRightNode(root.left, k,
                             level + 1, value_level)
 
    # if node is found in left subtree,
    # return it
    if (leftNode):
        return leftNode
 
    # recurse for right subtree by
    # increasing level by 1
    return nextRightNode(root.right, k,
                         level + 1, value_level)
 
# Function to find next node of given node
# in the same level in given binary tree
def nextRightNodeUtil(root, k):
    value_level = [0]
 
    return nextRightNode(root, k, 1, value_level)
 
# A utility function to test above functions
def test(root, k):
    nr = nextRightNodeUtil(root, k)
    if (nr != None):
        print("Next Right of", k, "is", nr.key)
    else:
        print("No next right node found for", k)
 
# Driver Code
if __name__ == '__main__':
     
    # Let us create binary tree given in the
    # above example
    root = newNode(10)
    root.left = newNode(2)
    root.right = newNode(6)
    root.right.right = newNode(5)
    root.left.left = newNode(8)
    root.left.right = newNode(4)
 
    test(root, 10)
    test(root, 2)
    test(root, 6)
    test(root, 5)
    test(root, 8)
    test(root, 4)
 
# This code is contributed by PranchalK

C#




/* C# program to find next right of a given key
using preorder traversal */
using System;
 
class GfG
{
     
public class V
{
    public int value_level = 0;
}
 
// A Binary Tree Node
public class Node
{
    public Node left, right;
    public int key;
}
 
// Utility function to create a new tree node
static Node newNode(int key)
{
    Node temp = new Node();
    temp.key = key;
    temp.left = null;
    temp.right = null;
    return temp;
}
 
// Function to find next node for given node
// in same level in a binary tree by using
// pre-order traversal
static Node nextRightNode(Node root, int k,
                            int level, V value)
{
    // return null if tree is empty
    if (root == null)
        return null;
 
    // if desired node is found, set
    // value_level to current level
    if (root.key == k)
    {
        value.value_level = level;
        return null;
    }
 
    // if value_level is already set, then current
    // node is the next right node
    else if (value.value_level != 0)
    {
        if (level == value.value_level)
            return root;
    }
 
    // recurse for left subtree by increasing level by 1
    Node leftNode = nextRightNode(root.left,
                            k, level + 1, value);
 
    // if node is found in left subtree, return it
    if (leftNode != null)
        return leftNode;
 
    // recurse for right subtree by
    // increasing level by 1
    return nextRightNode(root.right, k,
                       level + 1, value);
}
 
// Function to find next node of given node in the
// same level in given binary tree
static Node nextRightNodeUtil(Node root, int k)
{
    V v = new V();
 
    return nextRightNode(root, k, 1, v);
}
 
// A utility function to test above functions
static void test(Node root, int k)
{
    Node nr = nextRightNodeUtil(root, k);
    if (nr != null)
        Console.WriteLine("Next Right of " +
                            k + " is "+ nr.key);
    else
        Console.WriteLine("No next right node" +
                            " found for " + k);
}
 
// Driver main
public static void Main(String[] args)
{
    // Let us create binary tree given in the
    // above example
    Node root = newNode(10);
    root.left = newNode(2);
    root.right = newNode(6);
    root.right.right = newNode(5);
    root.left.left = newNode(8);
    root.left.right = newNode(4);
 
    test(root, 10);
    test(root, 2);
    test(root, 6);
    test(root, 5);
    test(root, 8);
    test(root, 4);
}
}
 
// This code contributed by Rajput-Ji

Javascript




<script>
 
    /* Javascript program to find next right of a given key
    using preorder traversal */
     
    // A Binary Tree Node
    class Node
    {
        constructor(key) {
           this.left = null;
           this.right = null;
           this.key = key;
        }
    }
 
    // Utility function to create a new tree node
    function newNode(key)
    {
        let temp = new Node(key);
        return temp;
    }
 
    // Function to find next node for given node
    // in same level in a binary tree by using
    // pre-order traversal
    function nextRightNode(root, k, level, value)
    {
        // return null if tree is empty
        if (root == null)
            return null;
 
        // if desired node is found, set value[0]
        // to current level
        if (root.key == k) {
            value[0] = level;
            return null;
        }
 
        // if value[0] is already set, then current
        // node is the next right node
        else if (value[0] != 0) {
            if (level == value[0])
                return root;
        }
 
        // recurse for left subtree by increasing level by 1
        let leftNode = nextRightNode(root.left, k, level + 1, value);
 
        // if node is found in left subtree, return it
        if (leftNode != null)
            return leftNode;
 
        // recurse for right subtree by increasing level by 1
        return nextRightNode(root.right, k, level + 1, value);
    }
 
    // Function to find next node of given node in the
    // same level in given binary tree
    function nextRightNodeUtil(root, k)
    {
 
        let v = new Array(1);
        v[0] = 0;
        return nextRightNode(root, k, 1, v);
    }
 
    // A utility function to test above functions
    function test(root, k)
    {
        let nr = nextRightNodeUtil(root, k);
        if (nr != null)
            document.write("Next Right of " + k + " is "+ nr.key +
            "</br>");
        else
            document.write("No next right node found for " + k +
            "</br>");
    }
     
    // Let us create binary tree given in the
    // above example
    let root = newNode(10);
    root.left = newNode(2);
    root.right = newNode(6);
    root.right.right = newNode(5);
    root.left.left = newNode(8);
    root.left.right = newNode(4);
  
    test(root, 10);
    test(root, 2);
    test(root, 6);
    test(root, 5);
    test(root, 8);
    test(root, 4);
   
</script>

Output

No next right node found for 10
Next Right of 2 is 6
No next right node found for 6
No next right node found for 5
Next Right of 8 is 4
Next Right of 4 is 5

Time Complexity: O(n) 
Auxiliary Space: O(1) 

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