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Print nodes at k distance from root | Iterative
  • Difficulty Level : Easy
  • Last Updated : 02 Nov, 2020

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

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



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


This article is contributed by Mandeep Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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