program to count leaf nodes in a binary tree in java

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This is 8th part of java binary tree tutorial.

Java Binary tree tutorial:

    Binary tree in java Binary tree preorder traversal Binary tree postorder traversal Binary tree inorder traversal Binary tree level order traversal Binary tree spiral order traversal Print leaf nodes of binary tree Count leaf nodes in binary tree Print all paths from root to leaf in binary tree Print vertical sum of binary tree in java Get level of node in binary tree in java

In this post, we will see about program to count leaf nodes in a binary tree in java

Algorithm-

Steps for counting number of leaf nodes are:
  • If node is null then return 0
  • If encountered leaf node(i.e. node.left is null and node.right is null) then return 1.
  • Recursively calculate number of leaf nodes using
  • Number of leaf nodes= number of leaf nodes in left subtree + number of leaf nodes in right sub tree
    
Code for recursion will be:
/* To get the count of leaf nodes in a binary tree*/
 public static  int getLeafCountOfBinaryTree(TreeNode node)
 {
   if(node == null)      
     return 0;
   if(node.left ==null && node.right==null)     
     return 1;           
   else
     return getLeafCountOfBinaryTree(node.left)+ getLeafCountOfBinaryTree(node.right);     
}


Lets create java program for counting number of leaf nodes:
 
package org.arpit.java2blog;

public class BinaryTree {

 
 public static class TreeNode
 {
  int data;
  TreeNode left;
  TreeNode right;
  TreeNode(int data)
  {
   this.data=data;
  }
 }
 
 // Recursive Solution
/* To get the count of leaf nodes in a binary tree*/
public static  int getLeafCountOfBinaryTree(TreeNode node)
{
  if(node == null)      
    return 0;
  if(node.left ==null && node.right==null)     
    return 1;           
  else
    return getLeafCountOfBinaryTree(node.left)+ getLeafCountOfBinaryTree(node.right);     
}

 
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  TreeNode rootNode=createBinaryTree();
  System.out.println("Number of leaf nodes in binary tree :"+getLeafCountOfBinaryTree(rootNode));
 }
 
 public static TreeNode createBinaryTree()
 {
  
  TreeNode rootNode =new TreeNode(40);
  TreeNode node20=new TreeNode(20);
  TreeNode node10=new TreeNode(10);
  TreeNode node30=new TreeNode(30);
  TreeNode node60=new TreeNode(60);
  TreeNode node50=new TreeNode(50);
  TreeNode node70=new TreeNode(70);
  
  rootNode.left=node20;
  rootNode.right=node60;
  
  node20.left=node10;
  node20.right=node30;
  
  node60.left=node50;
  node60.right=node70;
  
  return rootNode;
 }
}

Run above program and you will get following output:
 
Number of leaf nodes in binary tree :4

Please go through Frequently asked java interview programs  for more such programs.

Written by Arpit:

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