If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.
This is 1st part of 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

A binary tree is a tree data structure in which each node has at most two children, which are referred to as the left child and the right child

Example of binary tree:

I have posted various programs on binary tree so that you can practice them for interviews and it will also help in understanding recursion.

Binary tree traversals:

PreOrder traversal - In PreOrder traversal,each node is processed before either of its sub-trees.In simpler words,Visit each node before its children.

InOrder traversal : In InOrder traversal,each node is processed between subtrees.In simpler words,Visit left subtree, node and then right subtree.

PostOrder traversal: In PostOrder traversal,each node is processed after subtrees traversal.In simpler words,Visit left subtree,  right subtree and then node.
Level order traversal : In Level order traversal, tree is traversed by each level. It is same as breadth first search.

Spiral/Zigzag order traversal : In spiral order traversal, tree is traversed in spiral shape.
Binary tree reverse level order traversal: It is similar to level order but in reverse
Binary tree boundary traversal : This traversal traverse boundary of binary tree

Other Binary tree programs:




If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.
This is 9th part of java binary tree tutorial.

In this post, we will see about program to print all paths from root to leaf in a binary tree in java.
Below diagram will show all paths  from root to leaf:

Algorithm:

Steps for print all paths from root to leaf are:
  • If node is null then return 0
  • put node.data in array and increment len by 1.
  • If encounterd leaf node(i.e. node.left is null and node.right is null) then print array.
  • Recursively visit left subtree and right subtree
Code for recursion will be:
// Prints all paths to leaf
 public static void printAllPathsToLeaf(TreeNode node, int[] path, int len) {
     if ( node == null )
         return;

     // storing data in array
     path[len] = node.data;
     len++;

     if(node.left == null && node.right == null) {
         // leaf node is reached
         printArray(path,len);
         return;
     }

     printAllPathsToLeaf(node.left, path, len);
     printAllPathsToLeaf(node.right, path, len);
 }


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;
  }
 }
 
// Prints all paths to leaf
 public static void printAllPathsToLeaf(TreeNode node, int[] path, int len) {
     if ( node == null )
         return;

     // storing data in array
     path[len] = node.data;
     len++;

     if(node.left == null && node.right == null) {
         // leaf node is reached
         printArray(path,len);
         return;
     }

     printAllPathsToLeaf(node.left, path, len);
     printAllPathsToLeaf(node.right, path, len);
 }

 
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  TreeNode rootNode=createBinaryTree();
  System.out.println("Printing all paths from root to leaf :");
  printAllPathsToLeaf(rootNode,new int[1000],0);
 }

public static void  printArray(int[] path,int len)
 {
  for (int i = 0; i < len; i++) {
  System.out.print(" "+path[i]);
 }
  System.out.println();
 }
 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 all paths from root to leaf :
40 20 10 5 
40 20 30 
40 60 50 55 
40 60 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

Please go through java interview programs for more such programs.

If you want to practice data structure and algorithm programs, you can go through data structure and algorithm interview questions.
This is 6th part of java binary tree tutorial.

In this post, we will see about Spiral/Zigzag Level Order binary tree traversal in java.

Spiral/Zigzag Level Order traversal:

 Spiral/Zigzag Level order traversal of below tree will be:


Steps for solution:
  1. Create an empty stack s and push root to it.
  2. while stack is not NULL Do following
    1. Create a empty stack called tempStack.
    2. Pop a node from stack and push it to tempStack depending on directionFlag
    3. Change directionFlag to change the direction of traversal
    4. set stack=tempStack

 
// prints in Spiral/Zigzag level order
 public static void spiralOrZigzagLevelOrder(TreeNode root) {
        if(root==null) return; 
        Stack<TreeNode> stack=new Stack<TreeNode>();
        stack.push(root);
        
        boolean directionflag=false;
        while(!stack.isEmpty())
        {
            Stack<TreeNode> tempStack=new Stack<TreeNode>();
        
            while(!stack.isEmpty())
            {
                TreeNode tempNode=stack.pop();
             System.out.printf("%d ",tempNode.data);
                if(!directionflag) 
                {
                    if(tempNode.left!=null) 
                     tempStack.push(tempNode.left);
                    if(tempNode.right!=null) 
                     tempStack.push(tempNode.right);
                }else
                {
                    if(tempNode.right!=null) 
                     tempStack.push(tempNode.right);
                    if(tempNode.left!=null) 
                     tempStack.push(tempNode.left);
                }
            }
            // for changing direction
            directionflag=!directionflag; 
      
            stack=tempStack; 
        }
     
    }

Example:
Lets say your binary tree is :


So Spiral/Zigzag Level Order traversal will work as below:

Lets create java program for Spiral/Zigzag Level traversal:
 
package org.arpit.java2blog;

import java.util.Queue;
import java.util.LinkedList;
public class BinaryTree {

 
 public static class TreeNode
 {
  int data;
  TreeNode left;
  TreeNode right;
  TreeNode(int data)
  {
   this.data=data;
  }
 }
 
// prints spiral/zigzag level order
 public static void spiralOrZigzagLevelOrder(TreeNode root) {
        if(root==null) return; 
        Stack<TreeNode> stack=new Stack<TreeNode>();
        stack.push(root);
        
        boolean directionflag=false;
        while(!stack.isEmpty())
        {
            Stack<TreeNode> tempStack=new Stack<TreeNode>();
        
            while(!stack.isEmpty())
            {
                TreeNode tempNode=stack.pop();
             System.out.printf("%d ",tempNode.data);
                if(!directionflag) 
                {
                    if(tempNode.left!=null) 
                     tempStack.push(tempNode.left);
                    if(tempNode.right!=null) 
                     tempStack.push(tempNode.right);
                }else
                {
                    if(tempNode.right!=null) 
                     tempStack.push(tempNode.right);
                    if(tempNode.left!=null) 
                     tempStack.push(tempNode.left);
                }
            }
            // for changing direction
            directionflag=!directionflag; 
      
            stack=tempStack; 
        }
     
    }
 public static void main(String[] args)
 {
  BinaryTree bi=new BinaryTree();
  // Creating a binary tree
  TreeNode rootNode=createBinaryTree();
  System.out.println("Spiral/Zigzag traversal of binary tree :");
  spiralOrZigzagLevelOrder(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:
 
Spiral/Zigzag traversal of binary tree :
40 60 20 10 30 50 70 55 5 

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

Please go through java interview programs for more such programs.
 

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