Traversals.java

package Trees;

/*
 * Travelling each and every element at least once.
 * The space complexity for traversals of any binary tree is O(h), h is height.
 * All these are Depth First Search Traversals (DFS).
 */
public class Traversals {

    /*
     * To do preorder traversal that is work -> left -> right.
     */
    public static void preorder(Node root) {
        if (root == null)
            return;
        System.out.print(root.val + " ");
        preorder(root.left);
        preorder(root.right);
    }

    /*
     * To do inorder traversal that is left -> work -> right.
     */
    public static void inorder(Node root) {
        if (root == null)
            return;
        inorder(root.left);
        System.out.print(root.val + " ");
        inorder(root.right);
    }

    /*
     * To do postorder traversal that is left -> right -> work.
     */
    public static void postorder(Node root) {
        if (root == null)
            return;
        postorder(root.left);
        postorder(root.right);
        System.out.print(root.val + " ");
    }

    public static void main(String[] args) {
        // Creating a Binary Tree to display values and do traversals.
        Node root = new Node(10);
        Node a = new Node(20);
        Node b = new Node(30);
        root.left = a;
        root.right = b;

        Node c = new Node(40);
        Node d = new Node(50);
        a.left = c;
        a.right = d;

        Node e = new Node(60);
        Node f = new Node(70);
        b.right = e;
        e.right = f;

        preorder(root);
        System.out.println();
        inorder(root);
        System.out.println();
        postorder(root);
    }
}