TreeTraversal.java

public class TreeTraversal {
    static class Node {
        int data;
        Node left;
        Node right;

        Node(int data) {
            this.data = data;
            this.left = null;
            this.right = null;
        }
    }

    static class BinaryTree {
        static int index = -1;

        public Node BuildTree(int nodes[]) {
            index++;
            if (nodes[index] == -1) {
                return null;
            }
            Node newNode = new Node(nodes[index]);
            newNode.left = BuildTree(nodes);
            newNode.right = BuildTree(nodes);
            return newNode;
        }
    }

    public static void preorder(Node root) {
        if (root == null) {
            return;
        }
        System.out.print(root.data + " ");
        preorder(root.left);
        preorder(root.right);
    }

    public static void inorder(Node root) {
        if (root == null) {
            return;
        }
        inorder(root.left);
        System.out.print(root.data + " ");
        inorder(root.right);
    }

    public static void postorder(Node root) {
        if (root == null) {
            return;
        }
        postorder(root.left);
        postorder(root.right);
        System.out.print(root.data + " ");
    }

    public static void main(String[] args) {
        int nodes[] = { 1, 2, 4, -1, -1, 5, -1, -1, 3, -1, 6, -1, -1 };
        BinaryTree tree = new BinaryTree();
        Node root = tree.BuildTree(nodes);
        System.out.print("ROOT NODE -> ");
        System.out.println(root.data);
        System.out.print("PREORDER TRAVERSAL -> ");
        preorder(root);
        System.out.println("");
        System.out.print("INORDER TRAVERSAL -> ");
        inorder(root);
        System.out.println("");
        System.out.print("POST-ORDER TRAVERSAL -> ");
        postorder(root);
        System.out.println("");
    }
}