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Print nodes at k distance from root | Iterative

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

Given a root of a tree, and an integer k. Print all the nodes which are at k distance from root.
Example :
 

Input :
                20
              /   \
            10    30
           / \    / \
          5  15  25  40
             /
            12

and k = 3
Root is at level 1.

Output :
5 15 25 40

 

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Recursive approach to this problem is discussed here 
Following is the iterative approach. 
The solution is similar to Getting level of node in Binary Tree 
 



C++




// CPP program to print all nodes of level k
// iterative approach
/* binary tree
root is at level 1
 
                20
              /   \
            10    30
           / \    / \
          5  15  25  40
             /
            12  */
#include <bits/stdc++.h>
using namespace std;
 
// Node of binary tree
struct Node {
    int data;
    Node* left, * right;
};
 
// Function to add a new node
Node* newNode(int data)
{
    Node* newnode = new Node();
    newnode->data = data;
    newnode->left = newnode->right = NULL;
}
 
// Function to print nodes of given level
bool printKDistant(Node* root, int klevel)
{
    queue<Node*> q;
    int level = 1;
    bool flag = false;
    q.push(root);
 
    // extra NULL is pushed to keep track
    // of all the nodes to be pushed before
    // level is incremented by 1
    q.push(NULL);
    while (!q.empty()) {
        Node* temp = q.front();
 
        // print when level is equal to k
        if (level == klevel && temp != NULL) {
            flag = true;
            cout << temp->data << " ";
        }
        q.pop();
        if (temp == NULL) {
            if (q.front())
                q.push(NULL);
            level += 1;
 
            // break the loop if level exceeds
            // the given level number
            if (level > klevel)
                break;
        } else {
            if (temp->left)
                q.push(temp->left);
 
            if (temp->right)
                q.push(temp->right);
        }
    }
    cout << endl;
 
    return flag;
}
 
// Driver code
int main()
{
    // create a binary tree
    Node* root = newNode(20);
    root->left = newNode(10);
    root->right = newNode(30);
    root->left->left = newNode(5);
    root->left->right = newNode(15);
    root->left->right->left = newNode(12);
    root->right->left = newNode(25);
    root->right->right = newNode(40);
 
    cout << "data at level 1 : ";
    int ret = printKDistant(root, 1);
    if (ret == false)
        cout << "Number exceeds total number of levels\n";
 
    cout << "data at level 2 : ";
    ret = printKDistant(root, 2);
    if (ret == false)
        cout << "Number exceeds total number of levels\n";
 
    cout << "data at level 3 : ";
    ret = printKDistant(root, 3);
    if (ret == false)
        cout << "Number exceeds total number of levels\n";
 
    cout << "data at level 6 : ";
    ret = printKDistant(root, 6);
    if (ret == false)
        cout << "Number exceeds total number of levels\n";
 
    return 0;
}

Java




// Java program to print all nodes of level k
// iterative approach
/* binary tree
root is at level 1
 
                20
            / \
            10 30
        / \ / \
        5 15 25 40
            /
            12 */
             
import java.util.*;
class GFG
{
 
// Node of binary tree
static class Node
{
    int data;
    Node left, right;
}
 
// Function to add a new node
static Node newNode(int data)
{
    Node newnode = new Node();
    newnode.data = data;
    newnode.left = newnode.right = null;
    return newnode;
}
 
// Function to print nodes of given level
static boolean printKDistant(Node root, int klevel)
{
    Queue<Node> q = new LinkedList<>();
    int level = 1;
    boolean flag = false;
    q.add(root);
 
    // extra null is added to keep track
    // of all the nodes to be added before
    // level is incremented by 1
    q.add(null);
    while (q.size() > 0)
    {
        Node temp = q.peek();
 
        // print when level is equal to k
        if (level == klevel && temp != null)
        {
            flag = true;
            System.out.print( temp.data + " ");
        }
        q.remove();
        if (temp == null)
        {
            if (q.peek() != null)
                q.add(null);
            level += 1;
 
            // break the loop if level exceeds
            // the given level number
            if (level > klevel)
                break;
        }
        else
        {
            if (temp.left != null)
                q.add(temp.left);
 
            if (temp.right != null)
                q.add(temp.right);
        }
    }
    System.out.println();
    return flag;
}
 
// Driver code
public static void main(String srga[])
{
    // create a binary tree
    Node root = newNode(20);
    root.left = newNode(10);
    root.right = newNode(30);
    root.left.left = newNode(5);
    root.left.right = newNode(15);
    root.left.right.left = newNode(12);
    root.right.left = newNode(25);
    root.right.right = newNode(40);
 
    System.out.print( "data at level 1 : ");
    boolean ret = printKDistant(root, 1);
    if (ret == false)
        System.out.print( "Number exceeds total " +
                            "number of levels\n");
 
    System.out.print("data at level 2 : ");
    ret = printKDistant(root, 2);
    if (ret == false)
        System.out.print("Number exceeds total " +
                            "number of levels\n");
 
    System.out.print( "data at level 3 : ");
    ret = printKDistant(root, 3);
    if (ret == false)
        System.out.print("Number exceeds total " +
                        "number of levels\n");
 
    System.out.print( "data at level 6 : ");
    ret = printKDistant(root, 6);
    if (ret == false)
        System.out.print( "Number exceeds total" +
                            "number of levels\n");
 
}
}
 
// This code is contributed by Arnab Kundu

Python3




# Python3 program to print all nodes of level k
# iterative approach
""" binary tree
root is at level 1
 
                20
            / \
            10 30
        / \ / \
        5 15 25 40
            /
            12 """
 
# Node of binary tree
# Function to add a new node
class newNode:
    def __init__(self, data):
        self.data = data
        self.left = self.right = None
         
# Function to prnodes of given level
def printKDistant( root, klevel):
 
    q = []
    level = 1
    flag = False
    q.append(root)
 
    # extra None is appended to keep track
    # of all the nodes to be appended
    # before level is incremented by 1
    q.append(None)
    while (len(q)):
        temp = q[0]
 
        # prwhen level is equal to k
        if (level == klevel and temp != None):
            flag = True
            print(temp.data, end = " ")
         
        q.pop(0)
        if (temp == None) :
            if (len(q)):
                q.append(None)
            level += 1
 
            # break the loop if level exceeds
            # the given level number
            if (level > klevel) :
                break
        else:
            if (temp.left) :
                q.append(temp.left)
 
            if (temp.right) :
                q.append(temp.right)
    print()
 
    return flag
     
# Driver Code
if __name__ == '__main__':
    root = newNode(20)
    root.left = newNode(10)
    root.right = newNode(30)
    root.left.left = newNode(5)
    root.left.right = newNode(15)
    root.left.right.left = newNode(12)
    root.right.left = newNode(25)
    root.right.right = newNode(40)
 
    print("data at level 1 : ", end = "")
    ret = printKDistant(root, 1)
    if (ret == False):
        print("Number exceeds total",
                  "number of levels")
 
    print("data at level 2 : ", end = "")
    ret = printKDistant(root, 2)
    if (ret == False) :
        print("Number exceeds total",
                  "number of levels")
 
    print("data at level 3 : ", end = "")
    ret = printKDistant(root, 3)
    if (ret == False) :
        print("Number exceeds total",
                  "number of levels")
 
    print("data at level 6 : ", end = "")
    ret = printKDistant(root, 6)
    if (ret == False):
        print("Number exceeds total number of levels")
 
# This code is contributed
# by SHUBHAMSINGH10

C#




// C# program to print all nodes of level k
// iterative approach
/* binary tree
root is at level 1
 
                20
            / \
            10 30
        / \ / \
        5 15 25 40
            /
            12 */
             
using System;
using System.Collections.Generic;
 
class GFG
{
 
// Node of binary tree
public class Node
{
    public int data;
    public Node left, right;
}
 
// Function to add a new node
static Node newNode(int data)
{
    Node newnode = new Node();
    newnode.data = data;
    newnode.left = newnode.right = null;
    return newnode;
}
 
// Function to print nodes of given level
static Boolean printKDistant(Node root, int klevel)
{
    Queue<Node> q = new Queue<Node>();
    int level = 1;
    Boolean flag = false;
    q.Enqueue(root);
 
    // extra null is added to keep track
    // of all the nodes to be added before
    // level is incremented by 1
    q.Enqueue(null);
    while (q.Count > 0)
    {
        Node temp = q.Peek();
 
        // print when level is equal to k
        if (level == klevel && temp != null)
        {
            flag = true;
            Console.Write( temp.data + " ");
        }
        q.Dequeue();
        if (temp == null)
        {
            if (q.Count > 0&&q.Peek() != null)
                q.Enqueue(null);
            level += 1;
 
            // break the loop if level exceeds
            // the given level number
            if (level > klevel)
                break;
        }
        else
        {
            if (temp.left != null)
                q.Enqueue(temp.left);
 
            if (temp.right != null)
                q.Enqueue(temp.right);
        }
    }
    Console.Write("\n");
    return flag;
}
 
// Driver code
public static void Main(String []srga)
{
    // create a binary tree
    Node root = newNode(20);
    root.left = newNode(10);
    root.right = newNode(30);
    root.left.left = newNode(5);
    root.left.right = newNode(15);
    root.left.right.left = newNode(12);
    root.right.left = newNode(25);
    root.right.right = newNode(40);
 
    Console.Write( "data at level 1 : ");
    Boolean ret = printKDistant(root, 1);
    if (ret == false)
        Console.Write( "Number exceeds total " +
                            "number of levels\n");
 
    Console.Write("data at level 2 : ");
    ret = printKDistant(root, 2);
    if (ret == false)
        Console.Write("Number exceeds total " +
                            "number of levels\n");
 
    Console.Write( "data at level 3 : ");
    ret = printKDistant(root, 3);
    if (ret == false)
        Console.Write("Number exceeds total " +
                        "number of levels\n");
 
    Console.Write( "data at level 6 : ");
    ret = printKDistant(root, 6);
    if (ret == false)
        Console.Write( "Number exceeds total" +
                            "number of levels\n");
 
}
}
 
// This code is contributed by Princi Singh

Javascript




<script>
    // Javascript program to print all nodes of level k
    // iterative approach
    /* binary tree
    root is at level 1
 
                    20
                / \
                10 30
            / \ / \
            5 15 25 40
                /
                12 */
     
    class Node
    {
        constructor(data) {
           this.left = null;
           this.right = null;
           this.data = data;
        }
    }
     
    // Function to add a new node
    function newNode(data)
    {
        let newnode = new Node(data);
        return newnode;
    }
 
    // Function to print nodes of given level
    function printKDistant(root, klevel)
    {
        let q = [];
        let level = 1;
        let flag = false;
        q.push(root);
 
        // extra null is added to keep track
        // of all the nodes to be added before
        // level is incremented by 1
        q.push(null);
        while (q.length > 0)
        {
            let temp = q[0];
 
            // print when level is equal to k
            if (level == klevel && temp != null)
            {
                flag = true;
                document.write( temp.data + " ");
            }
            q.shift();
            if (temp == null)
            {
                if (q[0] != null)
                    q.push(null);
                level += 1;
 
                // break the loop if level exceeds
                // the given level number
                if (level > klevel)
                    break;
            }
            else
            {
                if (temp.left != null)
                    q.push(temp.left);
 
                if (temp.right != null)
                    q.push(temp.right);
            }
        }
        document.write("</br>");
        return flag;
    }
     
    // create a binary tree
    let root = newNode(20);
    root.left = newNode(10);
    root.right = newNode(30);
    root.left.left = newNode(5);
    root.left.right = newNode(15);
    root.left.right.left = newNode(12);
    root.right.left = newNode(25);
    root.right.right = newNode(40);
   
    document.write( "data at level 1 : ");
    let ret = printKDistant(root, 1);
    if (ret == false)
        document.write( "Number exceeds total " +
                            "number of levels" + "</br>");
   
    document.write("data at level 2 : ");
    ret = printKDistant(root, 2);
    if (ret == false)
        document.write("Number exceeds total " +
                            "number of levels" + "</br>");
   
    document.write( "data at level 3 : ");
    ret = printKDistant(root, 3);
    if (ret == false)
        document.write("Number exceeds total " +
                        "number of levels" + "</br>");
   
    document.write( "data at level 6 : ");
    ret = printKDistant(root, 6);
    if (ret == false)
        document.write( "Number exceeds total" +
                            "number of levels" + "</br>");
                            
// This code is contributed by suresh07.           
</script>

Output: 
 

data at level 1 : 20 
data at level 2 : 10 30 
data at level 3 : 5 15 25 40 
data at level 6 : 
Number exceeds total number of levels

 

?list=PLqM7alHXFySHCXD7r1J0ky9Zg_GBB1dbk 
This article is contributed by Mandeep Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 




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