how to print leaf nodes of a binary tree in java

This is 7th part of java binary tree tutorial.

In this post, we will see about program to print 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 encounterd leaf node(i.e. node.left is null and node.right is null) then print the node.
  • Recursively visit leaf subtree and right subtree.
Code for recursion will be:
 // print leaf nodes
 public static void printLeafNodes(TreeNode node) {
 
   if(node==null)
    return;
   
   if(node.left == null && node.right == null) {
    System.out.printf("%d ",node.data);
   }
   printLeafNodes(node.left);
   printLeafNodes(node.right);
 }



Example:
Binary tree:

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
 // print leaf nodes
 public static void printLeafNodes(TreeNode node) {
 
   if(node==null)
    return;
   
   if(node.left == null && node.right == null) {
    System.out.printf("%d ",node.data);
   }
   printLeafNodes(node.left);
   printLeafNodes(node.right);
 }


 
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  System.out.println("Printing leaf nodes in binary tree :");
  printLeafNodes(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);
  
 TreeNode node5=new TreeNode(5);
 TreeNode node55=new TreeNode(55);

 rootNode.left=node20;
 rootNode.right=node60;

 node20.left=node10;
 node20.right=node30;

 node60.left=node50;
 node60.right=node70;
 
 node10.left=node5;
 node50.right=node55;
 return rootNode;
 }
}

Run above program and you will get following output:
 
Printing leaf nodes in binary tree :
5 30 55 70 

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 Binary tree reverse level order traversal Binary tree boundary traversal Print leaf nodes of binary tree Count leaf nodes in binary tree get maximum element 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 Lowest common ancestor(LCA) in binary tree in java

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