JAVA program to do preorder,inorder,postorder traversals in a binary tree

ALGORITHM:

        We have 3 types of tree traversals

1. Preorder traversal
2. Inorder traversal
3. Postorder traversal

• In preorder traversal a node is visited then its left and right subtree is visite.
• In inorder traversal a node is visited after visiting its left subtree then it passes to the right subtree
• In postorder traversal a node is visited after its left and right subtree is visited or either of it or both are null.

 Algorithm in detail is in this link.

CODE:

//utility class for node

public class node{
    public int data;
    public node left,right;
    public node(){
        data=0;
        left=right=null;
    }
}

//class to implement the algorithm
import java.util.Scanner;

public class treeTraversals {

    static Scanner in = new Scanner(System.in);

    static node inputTree(){
        node temp=new node();
        System.out.print("Enter the value: ");
        temp.data=in.nextInt();
        System.out.print("Enter y if the node "+temp.data+" has left subtree: ");
        if(in.next().charAt(0)=='y')
            temp.left=inputTree();
        else
            temp.left=null;
        System.out.print("Enter y if the node "+temp.data+" has right subtree: ");
        if(in.next().charAt(0)=='y')
            temp.right=inputTree();
        else
            temp.right=null;
        return temp;
    }
    static void inorder(node tree){
        if(tree==null)
            return;
        inorder(tree.left);
        System.out.print(tree.data+"\t");
        inorder(tree.right);
    }

    static void preorder(node tree){
        if(tree==null)
            return;
        System.out.print(tree.data+"\t");
        preorder(tree.left);
        preorder(tree.right);
    }

    static void postorder(node tree){
        if(tree==null)
            return;
        postorder(tree.left);
        postorder(tree.right);
        System.out.print(tree.data+"\t");
    }

    public static void main(String[] args) {
        System.out.println("Enter the tree: ");
        node tree = new node();
        tree = inputTree();
        System.out.println("Inorder traversal ");
        inorder(tree);
        System.out.println("\nPreorder traversal ");
        preorder(tree);
        System.out.println("\nPostorder traversal ");
        postorder(tree);
    }
}

OUTPUT:

Enter the tree:
Enter the value: 2
Enter y if the node 2 has left subtree: y
Enter the value: 7
Enter y if the node 7 has left subtree: y
Enter the value: 2
Enter y if the node 2 has left subtree: n
Enter y if the node 2 has right subtree: n
Enter y if the node 7 has right subtree: y
Enter the value: 6
Enter y if the node 6 has left subtree: y
Enter the value: 5
Enter y if the node 5 has left subtree: n
Enter y if the node 5 has right subtree: n
Enter y if the node 6 has right subtree: y
Enter the value: 11
Enter y if the node 11 has left subtree: n
Enter y if the node 11 has right subtree: n
Enter y if the node 2 has right subtree: y
Enter the value: 5
Enter y if the node 5 has left subtree: n
Enter y if the node 5 has right subtree: y
Enter the value: 9
Enter y if the node 9 has left subtree: y
Enter the value: 4
Enter y if the node 4 has left subtree: n
Enter y if the node 4 has right subtree: n
Enter y if the node 9 has right subtree: n
Inorder traversal
2    7    5    6    11    2    5    4    9  
Preorder traversal
2    7    2    6    5    11    5    9    4  
Postorder traversal
2    5    11    6    7    4    9    5    2