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Print all nodes that are at distance k from a leaf node
  • Difficulty Level : Hard
  • Last Updated : 25 Jan, 2021

Given a Binary Tree and a positive integer k, print all nodes that are distance k from a leaf node. 
Here the meaning of distance is different from previous post. Here k distance from a leaf means k levels higher than a leaf node. For example if k is more than height of Binary Tree, then nothing should be printed. Expected time complexity is O(n) where n is the number nodes in the given Binary Tree.
 

distKfromLeaf

 

The idea is to traverse the tree. Keep storing all ancestors till we hit a leaf node. When we reach a leaf node, we print the ancestor at distance k. We also need to keep track of nodes that are already printed as output. For that we use a boolean array visited[].
  

C++




/* Program to print all nodes
which are at distance k from a leaf */
#include <iostream>
using namespace std;
#define MAX_HEIGHT 10000
 
struct Node {
    int key;
    Node *left, *right;
};
 
/* utility that allocates a new Node with the given key  */
Node* newNode(int key)
{
    Node* node = new Node;
    node->key = key;
    node->left = node->right = NULL;
    return (node);
}
 
/* This function prints all nodes that are distance k from a leaf node
   path[] --> Store ancestors of a node
   visited[] --> Stores true if a node is printed as output.  A node may be k
                 distance away from many leaves, we want to print it once */
void kDistantFromLeafUtil(Node* node, int path[], bool visited[],
                          int pathLen, int k)
{
    // Base case
    if (node == NULL)
        return;
 
    /* append this Node to the path array */
    path[pathLen] = node->key;
    visited[pathLen] = false;
    pathLen++;
 
    /* it's a leaf, so print the ancestor at distance k only
       if the ancestor is not already printed  */
    if (node->left == NULL &&
        node->right == NULL &&
        pathLen - k - 1 >= 0 &&
        visited[pathLen - k - 1] == false)
    {
        cout << path[pathLen - k - 1] << " ";
        visited[pathLen - k - 1] = true;
        return;
    }
 
    /* If not leaf node, recur for left and right subtrees */
    kDistantFromLeafUtil(node->left, path, visited, pathLen, k);
    kDistantFromLeafUtil(node->right, path, visited, pathLen, k);
}
 
/* Given a binary tree and a nuber k, print all nodes that are k
   distant from a leaf*/
void printKDistantfromLeaf(Node* node, int k)
{
    int path[MAX_HEIGHT];
    bool visited[MAX_HEIGHT] = { false };
    kDistantFromLeafUtil(node, path, visited, 0, k);
}
 
/* Driver code*/
int main()
{
    // Let us create binary tree
  // given in the above example
    Node* root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(3);
    root->left->left = newNode(4);
    root->left->right = newNode(5);
    root->right->left = newNode(6);
    root->right->right = newNode(7);
    root->right->left->right = newNode(8);
 
    cout << "Nodes at distance 2 are: ";
    printKDistantfromLeaf(root, 2);
 
    return 0;
}

Java




// Java program to print all nodes at a distance k from leaf
// A binary tree node
class Node {
    int data;
    Node left, right;
 
    Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
class BinaryTree {
    Node root;
 
    /* This function prints all nodes that are distance k from a leaf node
     path[] --> Store ancestors of a node
     visited[] --> Stores true if a node is printed as output.  A node may
     be k distance away from many leaves, we want to print it once */
    void kDistantFromLeafUtil(Node node, int path[], boolean visited[],
                              int pathLen, int k)
    {
        // Base case
        if (node == null)
            return;
 
        /* append this Node to the path array */
        path[pathLen] = node.data;
        visited[pathLen] = false;
        pathLen++;
 
        /* it's a leaf, so print the ancestor at distance k only
         if the ancestor is not already printed  */
        if (node.left == null && node.right == null
            && pathLen - k - 1 >= 0 && visited[pathLen - k - 1] == false) {
            System.out.print(path[pathLen - k - 1] + " ");
            visited[pathLen - k - 1] = true;
            return;
        }
 
        /* If not leaf node, recur for left and right subtrees */
        kDistantFromLeafUtil(node.left, path, visited, pathLen, k);
        kDistantFromLeafUtil(node.right, path, visited, pathLen, k);
    }
 
    /* Given a binary tree and a nuber k, print all nodes that are k
     distant from a leaf*/
    void printKDistantfromLeaf(Node node, int k)
    {
        int path[] = new int[1000];
        boolean visited[] = new boolean[1000];
        kDistantFromLeafUtil(node, path, visited, 0, k);
    }
 
    // Driver program to test the above functions
    public static void main(String args[])
    {
        BinaryTree tree = new BinaryTree();
 
        /* Let us construct the tree shown in above diagram */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
        tree.root.right.left.right = new Node(8);
 
        System.out.println(" Nodes at distance 2 are :");
        tree.printKDistantfromLeaf(tree.root, 2);
    }
}
 
// This code has been contributed by Mayank Jaiswal

Python3




# Program to print all nodes which are at
# distance k from a leaf
 
# utility that allocates a new Node with
# the given key
class newNode:
    def __init__(self, key):
        self.key = key
        self.left = self.right = None
 
# This function prints all nodes that
# are distance k from a leaf node
# path[] -. Store ancestors of a node
# visited[] -. Stores true if a node is
# printed as output. A node may be k distance
# away from many leaves, we want to print it once
def kDistantFromLeafUtil(node, path, visited,
                                 pathLen, k):
     
    # Base case
    if (node == None):
        return
 
    # append this Node to the path array
    path[pathLen] = node.key
    visited[pathLen] = False
    pathLen += 1
 
    # it's a leaf, so print the ancestor at
    # distance k only if the ancestor is
    # not already printed
    if (node.left == None and node.right == None and
                            pathLen - k - 1 >= 0 and
                            visited[pathLen - k - 1] == False):
        print(path[pathLen - k - 1], end = " ")
        visited[pathLen - k - 1] = True
        return
 
    # If not leaf node, recur for left
    # and right subtrees
    kDistantFromLeafUtil(node.left, path,
                         visited, pathLen, k)
    kDistantFromLeafUtil(node.right, path,
                         visited, pathLen, k)
 
# Given a binary tree and a nuber k,
# print all nodes that are k distant from a leaf
def printKDistantfromLeaf(node, k):
    global MAX_HEIGHT
    path = [None] * MAX_HEIGHT
    visited = [False] * MAX_HEIGHT
    kDistantFromLeafUtil(node, path, visited, 0, k)
 
# Driver Code
MAX_HEIGHT = 10000
 
# Let us create binary tree given in
# the above example
root = newNode(1)
root.left = newNode(2)
root.right = newNode(3)
root.left.left = newNode(4)
root.left.right = newNode(5)
root.right.left = newNode(6)
root.right.right = newNode(7)
root.right.left.right = newNode(8)
 
print("Nodes at distance 2 are:", end = " ")
printKDistantfromLeaf(root, 2)
 
# This code is contributed by pranchalK

C#




using System;
 
// C# program to print all nodes at a distance k from leaf
// A binary tree node
public class Node {
    public int data;
    public Node left, right;
 
    public Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
public class BinaryTree {
    public Node root;
 
    /* This function prints all nodes that are distance k from a leaf node
     path[] --> Store ancestors of a node
     visited[] --> Stores true if a node is printed as output.  A node may
     be k distance away from many leaves, we want to print it once */
    public virtual void kDistantFromLeafUtil(Node node, int[] path, bool[] visited, int pathLen, int k)
    {
        // Base case
        if (node == null) {
            return;
        }
 
        /* append this Node to the path array */
        path[pathLen] = node.data;
        visited[pathLen] = false;
        pathLen++;
 
        /* it's a leaf, so print the ancestor at distance k only
         if the ancestor is not already printed  */
        if (node.left == null && node.right == null && pathLen - k - 1 >= 0 && visited[pathLen - k - 1] == false) {
            Console.Write(path[pathLen - k - 1] + " ");
            visited[pathLen - k - 1] = true;
            return;
        }
 
        /* If not leaf node, recur for left and right subtrees */
        kDistantFromLeafUtil(node.left, path, visited, pathLen, k);
        kDistantFromLeafUtil(node.right, path, visited, pathLen, k);
    }
 
    /* Given a binary tree and a nuber k, print all nodes that are k
     distant from a leaf*/
    public virtual void printKDistantfromLeaf(Node node, int k)
    {
        int[] path = new int[1000];
        bool[] visited = new bool[1000];
        kDistantFromLeafUtil(node, path, visited, 0, k);
    }
 
    // Driver program to test the above functions
    public static void Main(string[] args)
    {
        BinaryTree tree = new BinaryTree();
 
        /* Let us construct the tree shown in above diagram */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
        tree.root.right.left.right = new Node(8);
 
        Console.WriteLine(" Nodes at distance 2 are :");
        tree.printKDistantfromLeaf(tree.root, 2);
    }
}
 
// This code is contributed by Shrikant13

Output: 

Nodes at distance 2 are: 1 3

Time Complexity: Time Complexity of above code is O(n) as the code does a simple tree traversal. 
Space Optimized Solution : 
 

C++




// C++  program to print all nodes at a distance k from leaf
// A binary tree node
#include <bits/stdc++.h>
using namespace std;
struct Node
{
  int data;
  Node *left, *right;
};
 
// Utility function to 
// create a new tree node  
Node* newNode(int key)  
{  
  Node *temp = new Node;  
  temp->data= key;  
  temp->left = temp->right = NULL;  
  return temp;  
}
 
/* Given a binary tree and a nuber k,
print all nodes that are k
distant from a leaf*/
int printKDistantfromLeaf(struct Node *node, int k)
{
  if (node == NULL)
    return -1;
  int lk = printKDistantfromLeaf(node->left, k);
  int rk = printKDistantfromLeaf(node->right, k);
  bool isLeaf = lk == -1 && lk == rk;
  if (lk == 0 || rk == 0 || (isLeaf && k == 0))
    cout<<(" " )<<( node->data);
  if (isLeaf && k > 0)
    return k - 1; // leaf node
  if (lk > 0 && lk < k)
    return lk - 1; // parent of left leaf
  if (rk > 0 && rk < k)
    return rk - 1; // parent of right leaf
  return -2;
}
 
// Driver code
int main()
{
  Node *root = NULL;
 
  /* Let us construct the tree shown in above diagram */
  root =  newNode(1);
  root->left =  newNode(2);
  root->right =  newNode(3);
  root->left->left =  newNode(4);
  root->left->right =  newNode(5);
  root->right->left =  newNode(6);
  root->right->right =  newNode(7);
  root->right->left->right =  newNode(8);
 
  cout << (" Nodes at distance 2 are :") << endl;
  printKDistantfromLeaf(root, 2);
}
 
// This code contributed by aashish1995

Java




// Java program to print all nodes at a distance k from leaf
// A binary tree node
class Node {
    int data;
    Node left, right;
 
    Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
class BinaryTree {
    Node root;
 
    /* Given a binary tree and a nuber k, print all nodes that are k
    distant from a leaf*/
    int printKDistantfromLeaf(Node node, int k)
    {
        if (node == null)
            return -1;
        int lk = printKDistantfromLeaf(node.left, k);
        int rk = printKDistantfromLeaf(node.right, k);
        boolean isLeaf = lk == -1 && lk == rk;
        if (lk == 0 || rk == 0 || (isLeaf && k == 0))
            System.out.print(" " + node.data);
        if (isLeaf && k > 0)
            return k - 1; // leaf node
        if (lk > 0 && lk < k)
            return lk - 1; // parent of left leaf
        if (rk > 0 && rk < k)
            return rk - 1; // parent of right leaf
 
        return -2;
    }
 
    // Driver program to test the above functions
    public static void main(String args[])
    {
        BinaryTree tree = new BinaryTree();
 
        /* Let us construct the tree shown in above diagram */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
        tree.root.right.left.right = new Node(8);
 
        System.out.println(" Nodes at distance 2 are :");
        tree.printKDistantfromLeaf(tree.root, 2);
    }
}
 
// This code has been contributed by Vijayan Annamalai

C#




// C# program to print all nodes at a distance k from leaf
// A binary tree node
using System;
 
class Node {
    public int data;
    public Node left, right;
  
    public Node(int item)
    {
        data = item;
        left = right = null;
    }
}
  
class BinaryTree {
     
    Node root;
  
    /* Given a binary tree and a nuber k, print all nodes that are k
    distant from a leaf*/
    int printKDistantfromLeaf(Node node, int k)
    {
        if (node == null)
            return -1;
        int lk = printKDistantfromLeaf(node.left, k);
        int rk = printKDistantfromLeaf(node.right, k);
        bool isLeaf = lk == -1 && lk == rk;
        if (lk == 0 || rk == 0 || (isLeaf && k == 0))
            Console.Write(" " + node.data);
        if (isLeaf && k > 0)
            return k - 1; // leaf node
        if (lk > 0 && lk < k)
            return lk - 1; // parent of left leaf
        if (rk > 0 && rk < k)
            return rk - 1; // parent of right leaf
  
        return -2;
    }
  
    // Driver program to test the above functions
    public static void Main(string []args)
    {
        BinaryTree tree = new BinaryTree();
  
        /* Let us construct the tree shown in above diagram */
        tree.root = new Node(1);
        tree.root.left = new Node(2);
        tree.root.right = new Node(3);
        tree.root.left.left = new Node(4);
        tree.root.left.right = new Node(5);
        tree.root.right.left = new Node(6);
        tree.root.right.right = new Node(7);
        tree.root.right.left.right = new Node(8);
  
        Console.Write("Nodes at distance 2 are :");
        tree.printKDistantfromLeaf(tree.root, 2);
    }
}
 
// This code is contributed by rutvik_56

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