Boundary traversal of binary tree in java

Table of Contents [hide]

Print left edge nodes (Excluding leaf nodes)
Print leaf nodes:
Print right edge nodes (From bottom to top) :

Java Binary tree tutorial:

If you want to practice data structure and algorithm programs, you can go through 100+ java coding interview questions.

In this post, we will see boundary traversal of binary tree in java.

Lets understand boundary traversal of binary tree with example:

If you look closely to above diagram, boundary traversals can be divided into three essential parts

Print left edge nodes (Excluding leaf nodes)
Print leaf nodes
Print right edge nodes (From bottom to top)

Print left edge nodes (Excluding leaf nodes)

If you define boundary for left part, it is nothing but left child if present, otherwise right child.

private static void printLeftEdgeNodes(TreeNode root) {
        if(root==null)
            return;

        // if leaf node, ignore while printing edges
        if(root.left==null && root.right==null)
            return;

        System.out.print(root.data+" ");

        // If left is null, right will be the boundary edge.
        if(root.left==null)
        {
            printLeftEdgeNodes(root.right);
        }
        else
        {
            printLeftEdgeNodes(root.left);
        }

    }

private static void printLeftEdgeNodes(TreeNode root) {

if(root==null)

return;

// if leaf node, ignore while printing edges

if(root.left==null && root.right==null)

return;

System.out.print(root.data+" ");

// If left is null, right will be the boundary edge.

if(root.left==null)

{

printLeftEdgeNodes(root.right);

}

else

{

printLeftEdgeNodes(root.left);

}

Print leaf nodes:

Its pretty simple operation. Whenever you encounter leaf node, print it.

private static void printLeafNodes(TreeNode root) {
        if(root==null)
            return;

        if(root.left==null && root.right==null)
        {
            System.out.print(root.data+" ");
            return;
        }
        printLeafNodes(root.left);
        printLeafNodes(root.right);
    }

private static void printLeafNodes(TreeNode root) {

if(root==null)

return;

if(root.left==null && root.right==null)

{

System.out.print(root.data+" ");

return;

}

printLeafNodes(root.left);

printLeafNodes(root.right);

}

You may also refer print leaf nodes of binary tree.

Print right edge nodes (From bottom to top) :

If you define boundary for right part, it is nothing but right child if present, otherwise left child. As we need to print bottom up, we will print the node while returning back from recursion stack.

private static void printRightBottomUp(TreeNode root)
    {
        if(root==null)
            return;

        // if leaf node, ignore while printing edges
        if(root.left==null && root.right==null)
        {
            return;
        }

        if(root.right!=null)
        {
            printRightBottomUp(root.right);
        }
        else if(root.left!=null)
        {
            printRightBottomUp(root.left);
        }

        System.out.print(root.data+" ");
    }

private static void printRightBottomUp(TreeNode root)

{

if(root==null)

return;

// if leaf node, ignore while printing edges

if(root.left==null && root.right==null)

{

return;

}

if(root.right!=null)

{

printRightBottomUp(root.right);

}

else if(root.left!=null)

{

printRightBottomUp(root.left);

}

System.out.print(root.data+" ");

}

Complete java program combining above three parts:

package org.arpit.java2blog.binarytree;

public class BinaryTreeBoundaryTraversal {
    public static class TreeNode
    {
        int data;
        TreeNode left;
        TreeNode right;
        TreeNode(int data)
        {
            this.data=data;
        }
    }

    public static void boundaryLevelTraversal(TreeNode root)
    {
        System.out.print(root.data+" ");
        printLeftEdgeNodes(root.left);
        printLeafNodes(root);
        printRightBottomUp(root.right);

    }

    private static void printLeafNodes(TreeNode root) {
        if(root==null)
            return;

        if(root.left==null && root.right==null)
        {
            System.out.print(root.data+" ");
            return;
        }
        printLeafNodes(root.left);
        printLeafNodes(root.right);
    }

    private static void printRightBottomUp(TreeNode root)
    {
        if(root==null)
            return;

        // if leaf node, ignore while printing edges
        if(root.left==null && root.right==null)
        {
            return;
        }

        if(root.right!=null)
        {
            printRightBottomUp(root.right);
        }
        else if(root.left!=null)
        {
            printRightBottomUp(root.left);
        }

        System.out.print(root.data+" ");
    }

    private static void printLeftEdgeNodes(TreeNode root) {
        if(root==null)
            return;

        // if leaf node, ignore while printing edges
        if(root.left==null && root.right==null)
            return;

        System.out.print(root.data+" ");

        // If left is null, right will be the boundary edge.
        if(root.left==null)
        {
            printLeftEdgeNodes(root.right);
        }
        else
        {
            printLeftEdgeNodes(root.left);
        }

    }

    public static void main(String[] args)
    {
        // Creating a binary tree
        TreeNode rootNode=createBinaryTree();
        System.out.println("Boundary traversal of binary tree will be:");
        boundaryLevelTraversal(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 node45=new TreeNode(45);
        TreeNode node55=new TreeNode(55);

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

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

        node60.left=node50;
        node60.right=node70;

        node10.right=node5;
        node5.right=node45;

        node50.right=node55;
        return rootNode;
    }
}

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package org.arpit.java2blog.binarytree;

public class BinaryTreeBoundaryTraversal {

public static class TreeNode

{

int data;

TreeNode left;

TreeNode right;

TreeNode(int data)

{

this.data=data;

}

public static void boundaryLevelTraversal(TreeNode root)

{

System.out.print(root.data+" ");

printLeftEdgeNodes(root.left);

printLeafNodes(root);

printRightBottomUp(root.right);

}

private static void printLeafNodes(TreeNode root) {

if(root==null)

return;

if(root.left==null && root.right==null)

{

System.out.print(root.data+" ");

return;

}

printLeafNodes(root.left);

printLeafNodes(root.right);

}

private static void printRightBottomUp(TreeNode root)

{

if(root==null)

return;

// if leaf node, ignore while printing edges

if(root.left==null && root.right==null)

{

return;

}

if(root.right!=null)

{

printRightBottomUp(root.right);

}

else if(root.left!=null)

{

printRightBottomUp(root.left);

}

System.out.print(root.data+" ");

}

private static void printLeftEdgeNodes(TreeNode root) {

if(root==null)

return;

// if leaf node, ignore while printing edges

if(root.left==null && root.right==null)

return;

System.out.print(root.data+" ");

// If left is null, right will be the boundary edge.

if(root.left==null)

{

printLeftEdgeNodes(root.right);

}

else

{

printLeftEdgeNodes(root.left);

}

public static void main(String[] args)

{

// Creating a binary tree

TreeNode rootNode=createBinaryTree();

System.out.println("Boundary traversal of binary tree will be:");

boundaryLevelTraversal(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 node45=new TreeNode(45);

TreeNode node55=new TreeNode(55);

rootNode.left=node20;

rootNode.right=node60;

node20.left=node10;

node20.right=node30;

node60.left=node50;

node60.right=node70;

node10.right=node5;

node5.right=node45;

node50.right=node55;

return rootNode;

}

When you run above program, you will get below output:

Boundary traversal of binary tree will be:
40 20 10 5 45 30 55 70 60

Boundary traversal of binary tree will be:

40 20 10 5 45 30 55 70 60

Java Binary tree tutorial:

Please go through java interview programs for more such programs.

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Comments

rich says:

December 19, 2016 at 7:07 am

node 45 is wrongly inserted into the tree in example.

1. arpitmandliya says:
  
  December 20, 2016 at 5:02 pm
  
  Hi Rich,
  It is binary tree not a binary search tree, so it does not matter where are you going to insert node 45.

Boundary traversal of binary tree in java

Print left edge nodes (Excluding leaf nodes)

Print leaf nodes:

Print right edge nodes (From bottom to top) :

Java Binary tree tutorial:

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Print left edge nodes (Excluding leaf nodes)

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