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pre-order, in-order & post-order traversal of binary tree
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‎CodingBlocks Training/Day20/treeTraversals.java‎

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package Lecture20;
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import java.util.Scanner;
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public class treeTraversals {
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private class Node {
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int data;
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Node left;
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Node right;
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Node(int data, Node left, Node right) {
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this.data = data;
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this.left = left;
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this.right = right;
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}
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}
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private Node root;
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private int size = 0;
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public treeTraversals() {
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Scanner sc = new Scanner(System.in);
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this.root = takeTreeInput(sc, null, false);
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}
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private Node takeTreeInput(Scanner sc, Node parent, boolean isLeftorRight) {
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if (parent == null) {
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System.out.print("Enter data for root node: ");
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} else {
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if (isLeftorRight) {
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System.out.print("Enter data for left child of " + parent.data + ": ");
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} else {
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System.out.print("Enter data for right child of: " + parent.data + ": ");
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}
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}
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int data = sc.nextInt();
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Node node = new Node(data, null, null);
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this.size++;
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boolean choice = false;
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System.out.print("Do you have left child for " + node.data + " -> true/false: ");
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choice = sc.nextBoolean();
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if (choice) {
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node.left = this.takeTreeInput(sc, node, true);
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}
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choice = false;
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System.out.print("Do you have right child for " + node.data + " -> true/false: ");
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choice = sc.nextBoolean();
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if (choice) {
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node.right = this.takeTreeInput(sc, node, false);
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}
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return node;
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}
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public void display() {
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this.display(this.root);
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}
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private void display(Node node) {
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if (node.left != null) {
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System.out.print(node.left.data + " => ");
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} else {
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System.out.print("END => ");
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}
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System.out.print(node.data);
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if (node.right != null) {
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System.out.print(" <= " + node.right.data);
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} else {
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System.out.print(" <= END");
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}
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System.out.println();
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if (node.left != null) {
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this.display(node.left);
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}
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if (node.right != null) {
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this.display(node.right);
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}
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}
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// tree traversals
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public void preOrder() {
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this.preOrder(this.root);
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}
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private void preOrder(Node node) { // NLR (node, left, right)
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if (node == null) {
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return;
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}
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System.out.print(node.data + " ");
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this.preOrder(node.left);
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this.preOrder(node.right);
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}
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public void inOrder() {
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this.inOrder(this.root);
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}
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private void inOrder(Node node) { // LNR
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if (node == null) {
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return;
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}
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this.inOrder(node.left);
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System.out.print(node.data + " ");
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this.inOrder(node.right);
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}
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public void postOrder() {
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this.postOrder(this.root);
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}
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private void postOrder(Node node) { // LRN
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if (node == null) {
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return;
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}
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this.postOrder(node.left);
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this.postOrder(node.right);
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System.out.print(node.data + " ");
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}
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public static void main(String[] args) {
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treeTraversals btree = new treeTraversals();
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System.out.println("\n-------------------------------\n");
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btree.display();
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System.out.println("\n-------------------------------------------");
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System.out.println("\n--------- pre-order traversal -------------\n");
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btree.preOrder();
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System.out.println();
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System.out.println("\n--------- in-order traversal -------------\n");
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btree.inOrder();
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System.out.println();
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System.out.println("\n--------- post-order traversal -------------\n");
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btree.postOrder();
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System.out.println();
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}
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}
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/* output:
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Enter data for root node: 50
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Do you have left child for 50 -> true/false: true
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Enter data for left child of 50: 25
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Do you have left child for 25 -> true/false: true
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Enter data for left child of 25: 12
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Do you have left child for 12 -> true/false: false
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Do you have right child for 12 -> true/false: false
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Do you have right child for 25 -> true/false: true
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Enter data for right child of: 25: 68
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Do you have left child for 68 -> true/false: false
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Do you have right child for 68 -> true/false: false
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Do you have right child for 50 -> true/false: true
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Enter data for right child of: 50: 75
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Do you have left child for 75 -> true/false: true
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Enter data for left child of 75: 39
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Do you have left child for 39 -> true/false: false
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Do you have right child for 39 -> true/false: false
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Do you have right child for 75 -> true/false: true
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Enter data for right child of: 75: 49
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Do you have left child for 49 -> true/false: false
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Do you have right child for 49 -> true/false: false
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-------------------------------
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25 => 50 <= 75
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12 => 25 <= 68
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END => 12 <= END
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END => 68 <= END
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39 => 75 <= 49
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END => 39 <= END
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END => 49 <= END
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-------------------------------------------
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--------- pre-order traversal -------------
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50 25 12 68 75 39 49
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--------- in-order traversal -------------
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12 25 68 50 39 75 49
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--------- post-order traversal -------------
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12 68 25 39 49 75 50
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*/

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