# Print all nodes in a binary tree having K leaves

Given a binary tree and a integer value K, the task is to find all nodes in given binary tree having K leaves in subtree rooted with them.

**Examples :**

// For above binary tree Input : k = 2 Output: {3} // here node 3 have k = 2 leaves Input : k = 1 Output: {6} // here node 6 have k = 1 leave

Here any node having K leaves means sum of leaves in left subtree and in right subtree must be equal to K. So to solve this problem we use Postorder traversal of tree. First we calculate leaves in left subtree then in right subtree and if sum is equal to K, then print current node. In each recursive call we return sum of leaves of left subtree and right subtree to it’s ancestor.

Below is the implementation of above approach:

## C++

// C++ program to count all nodes having k leaves // in subtree rooted with them #include<bits/stdc++.h> using namespace std; /* A binary tree node */ struct Node { int data ; struct Node * left, * right ; }; /* Helper function that allocates a new node with the given data and NULL left and right pointers. */ struct Node * newNode(int data) { struct Node * node = new Node; node->data = data; node->left = node->right = NULL; return (node); } // Function to print all nodes having k leaves int kLeaves(struct Node *ptr,int k) { // Base Conditions : No leaves if (ptr == NULL) return 0; // if node is leaf if (ptr->left == NULL && ptr->right == NULL) return 1; // total leaves in subtree rooted with this // node int total = kLeaves(ptr->left, k) + kLeaves(ptr->right, k); // Print this node if total is k if (k == total) cout << ptr->data << " "; return total; } // Driver program to run the case int main() { struct Node *root = newNode(1); root->left = newNode(2); root->right = newNode(4); root->left->left = newNode(5); root->left->right = newNode(6); root->left->left->left = newNode(9); root->left->left->right = newNode(10); root->right->right = newNode(8); root->right->left = newNode(7); root->right->left->left = newNode(11); root->right->left->right = newNode(12); kLeaves(root, 2); return 0; }

## Java

// Java program to count all nodes having k leaves // in subtree rooted with them class GfG { /* A binary tree node */ static class Node { int data ; Node left, right ; Node(int data) { this.data = data; } Node() { } } /* Helper function that allocates a new node with the given data and NULL left and right pointers. */ static Node newNode(int data) { Node node = new Node(); node.data = data; node.left = null; node.right = null; return (node); } // Function to print all nodes having k leaves static int kLeaves(Node ptr,int k) { // Base Conditions : No leaves if (ptr == null) return 0; // if node is leaf if (ptr.left == null && ptr.right == null) return 1; // total leaves in subtree rooted with this // node int total = kLeaves(ptr.left, k) + kLeaves(ptr.right, k); // Print this node if total is k if (k == total) System.out.print(ptr.data + " "); return total; } // Driver program to run the case public static void main(String[] args) { Node root = newNode(1); root.left = newNode(2); root.right = newNode(4); root.left.left = newNode(5); root.left.right = newNode(6); root.left.left.left = newNode(9); root.left.left.right = newNode(10); root.right.right = newNode(8); root.right.left = newNode(7); root.right.left.left = newNode(11); root.right.left.right = newNode(12); kLeaves(root, 2); } }

## Python3

# Python3 program to count all nodes # having k leaves in subtree rooted with them # A binary tree node has data, pointer to # left child and a pointer to right child # Helper function that allocates a new node # with the given data and None left and # right pointers class newNode: def __init__(self, data): self.data = data self.left = None self.right = None # Function to print all nodes having k leaves def kLeaves(ptr, k): # Base Conditions : No leaves if (ptr == None): return 0 # if node is leaf if (ptr.left == None and ptr.right == None): return 1 # total leaves in subtree rooted with this # node total = kLeaves(ptr.left, k) + \ kLeaves(ptr.right, k) # Prthis node if total is k if (k == total): print(ptr.data, end = " ") return total # Driver code root = newNode(1) root.left = newNode(2) root.right = newNode(4) root.left.left = newNode(5) root.left.right = newNode(6) root.left.left.left = newNode(9) root.left.left.right = newNode(10) root.right.right = newNode(8) root.right.left = newNode(7) root.right.left.left = newNode(11) root.right.left.right = newNode(12) kLeaves(root, 2) # This code is contributed by SHUBHAMSINGH10

## C#

// C# program to count all nodes having k leaves // in subtree rooted with them using System; class GfG { /* A binary tree node */ public class Node { public int data ; public Node left, right ; public Node(int data) { this.data = data; } public Node() { } } /* Helper function that allocates a new node with the given data and NULL left and right pointers. */ static Node newNode(int data) { Node node = new Node(); node.data = data; node.left = null; node.right = null; return (node); } // Function to print all nodes having k leaves static int kLeaves(Node ptr,int k) { // Base Conditions : No leaves if (ptr == null) return 0; // if node is leaf if (ptr.left == null && ptr.right == null) return 1; // total leaves in subtree rooted with this // node int total = kLeaves(ptr.left, k) + kLeaves(ptr.right, k); // Print this node if total is k if (k == total) Console.Write(ptr.data + " "); return total; } // Driver program to run the case public static void Main(String[] args) { Node root = newNode(1); root.left = newNode(2); root.right = newNode(4); root.left.left = newNode(5); root.left.right = newNode(6); root.left.left.left = newNode(9); root.left.left.right = newNode(10); root.right.right = newNode(8); root.right.left = newNode(7); root.right.left.left = newNode(11); root.right.left.right = newNode(12); kLeaves(root, 2); } } // This code has been contributed by 29AjayKumar

## Javascript

<script> // Javascript program to count all nodes having k leaves // in subtree rooted with them /* A binary tree node */ class Node { /* Helper function that allocates a new node with the given data and NULL left and right pointers. */ constructor(data) { this.data = data; this.left=this.right=null; } } // Function to print all nodes having k leaves function kLeaves(ptr,k) { // Base Conditions : No leaves if (ptr == null) return 0; // if node is leaf if (ptr.left == null && ptr.right == null) return 1; // total leaves in subtree rooted with this // node let total = kLeaves(ptr.left, k) + kLeaves(ptr.right, k); // Print this node if total is k if (k == total) document.write(ptr.data + " "); return total; } // Driver program to run the case let root = new Node(1); root.left = new Node(2); root.right = new Node(4); root.left.left = new Node(5); root.left.right = new Node(6); root.left.left.left = new Node(9); root.left.left.right = new Node(10); root.right.right = new Node(8); root.right.left = new Node(7); root.right.left.left = new Node(11); root.right.left.right = new Node(12); kLeaves(root, 2); // This code is contributed by rag2127 </script>

**Output:**

5 7

**Time complexity :** O(n)

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