Iterative program to count leaf nodes in a Binary Tree

Given a binary tree, count leaves in the tree without using recursion. A node is a leaf node if both left and right children of it are NULL.

  Example Tree  
 
Leaves count for the above tree is 3.

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

The idea is to use level order traversal. During traversal, if we find a node whose left and right children are NULL, we increment count.

C++

// C++ program to count leaf nodes in a Binary Tree 
#include <bits/stdc++.h> 
using namespace std; 
  
/* A binary tree Node has data, pointer to left 
   child  and a pointer to right child */
struct Node 
{ 
    int data; 
    struct Node* left, *right; 
}; 
  
/* Function to get the count of leaf Nodes in 
   a binary tree*/
unsigned int getLeafCount(struct Node* node) 
{ 
    // If tree is empty 
    if (!node) 
        return 0; 
  
    // Initialize empty queue. 
    queue<Node *> q; 
  
    // Do level order traversal starting from root 
    int count = 0; // Initialize count of leaves 
    q.push(node); 
    while (!q.empty()) 
    { 
        struct Node *temp = q.front(); 
        q.pop(); 
  
        if (temp->left != NULL) 
            q.push(temp->left); 
        if (temp->right != NULL) 
            q.push(temp->right); 
        if (temp->left == NULL && temp->right == NULL) 
            count++; 
    } 
    return count; 
} 
  
/* 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); 
} 
  
/* Driver program to test above functions*/
int main() 
{ 
    /*   1 
        /  \ 
      2     3 
     / \ 
    4   5 
    Let us create Binary Tree shown in  
    above example */
  
    struct Node *root = newNode(1); 
    root->left        = newNode(2); 
    root->right       = newNode(3); 
    root->left->left  = newNode(4); 
    root->left->right = newNode(5); 
  
    /* get leaf count of the above created tree */
    cout << getLeafCount(root); 
  
    return 0; 
} 

Java

// Java program to count leaf nodes 
// in a Binary Tree 
import java.util.*; 
  
class GFG  
{ 
    /* A binary tree Node has data,  
    pointer to left child and 
    a pointer to right child */
    static class Node  
    { 
        int data; 
        Node left, right; 
    } 
  
    /* Function to get the count of  
    leaf Nodes in a binary tree*/
    static int getLeafCount(Node node) 
    { 
        // If tree is empty 
        if (node == null) 
        { 
            return 0; 
        } 
  
        // Initialize empty queue. 
        Queue<Node> q = new LinkedList<>(); 
  
        // Do level order traversal starting from root 
        int count = 0; // Initialize count of leaves 
        q.add(node); 
        while (!q.isEmpty())  
        { 
            Node temp = q.peek(); 
            q.poll(); 
  
            if (temp.left != null)  
            { 
                q.add(temp.left); 
            } 
            if (temp.right != null) 
            { 
                q.add(temp.right); 
            } 
            if (temp.left == null &&  
                temp.right == null)  
            { 
                count++; 
            } 
        } 
        return count; 
    } 
  
    /* 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 = node.right = null; 
        return (node); 
    } 
  
    // Driver Code 
    public static void main(String[] args)  
    { 
        { 
            /*   1 
                / \ 
               2   3 
              / \ 
             4   5 
            Let us create Binary Tree shown in  
            above example */
            Node root = newNode(1); 
            root.left = newNode(2); 
            root.right = newNode(3); 
            root.left.left = newNode(4); 
            root.left.right = newNode(5); 
  
            /* get leaf count of the above created tree */
            System.out.println(getLeafCount(root)); 
        } 
    } 
} 
  
// This code is contributed by Rajput-Ji 

Python3

# Python3 program to count leaf nodes  
# in a Binary Tree  
from queue import Queue  
  
# 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 = self.right = None
          
# Function to get the count of leaf  
# Nodes in a binary tree 
def getLeafCount(node): 
      
    # If tree is empty  
    if (not node): 
        return 0
  
    # Initialize empty queue.  
    q = Queue() 
  
    # Do level order traversal  
    # starting from root  
    count = 0 # Initialize count of leaves  
    q.put(node)  
    while (not q.empty()): 
        temp = q.queue[0]  
        q.get() 
  
        if (temp.left != None): 
            q.put(temp.left)  
        if (temp.right != None): 
            q.put(temp.right)  
        if (temp.left == None and
            temp.right == None):  
            count += 1
    return count 
  
# Driver Code 
if __name__ == '__main__': 
      
    # 1  
    # / \  
    # 2 3  
    # / \  
    # 4 5  
    # Let us create Binary Tree shown  
    # in above example  
    root = newNode(1)  
    root.left = newNode(2)  
    root.right = newNode(3)  
    root.left.left = newNode(4)  
    root.left.right = newNode(5)  
  
    # get leaf count of the above  
    # created tree  
    print(getLeafCount(root)) 
  
# This code is contributed by PranchalK 

C#

// C# program to count leaf nodes 
// in a Binary Tree 
using System; 
using System.Collections.Generic;  
      
class GFG  
{ 
    /* A binary tree Node has data,  
    pointer to left child and 
    a pointer to right child */
    public class Node  
    { 
        public int data; 
        public Node left, right; 
    } 
  
    /* Function to get the count of  
    leaf Nodes in a binary tree*/
    static int getLeafCount(Node node) 
    { 
        // If tree is empty 
        if (node == null) 
        { 
            return 0; 
        } 
  
        // Initialize empty queue. 
        Queue<Node> q = new Queue<Node>(); 
  
        // Do level order traversal starting from root 
        int count = 0; // Initialize count of leaves 
        q.Enqueue(node); 
        while (q.Count!=0)  
        { 
            Node temp = q.Peek(); 
            q.Dequeue(); 
  
            if (temp.left != null)  
            { 
                q.Enqueue(temp.left); 
            } 
            if (temp.right != null) 
            { 
                q.Enqueue(temp.right); 
            } 
            if (temp.left == null &&  
                temp.right == null)  
            { 
                count++; 
            } 
        } 
        return count; 
    } 
  
    /* 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 = node.right = null; 
        return (node); 
    } 
  
    // Driver Code 
    public static void Main(String[] args)  
    { 
        { 
            /* 1 
                / \ 
            2 3 
            / \ 
            4 5 
            Let us create Binary Tree shown in  
            above example */
            Node root = newNode(1); 
            root.left = newNode(2); 
            root.right = newNode(3); 
            root.left.left = newNode(4); 
            root.left.right = newNode(5); 
  
            /* get leaf count of the above created tree */
            Console.WriteLine(getLeafCount(root)); 
        } 
    } 
} 
  
// This code is contributed by 29AjayKumar 

Output:

Time Complexity: O(n)

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My Personal Notes

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

C++

Java

Python3

C#

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