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

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

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);  
  
}  
}  

Output:

5 7

Time complexity : O(n)

This article is contributed by Shashank Mishra ( Gullu ). 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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