BSTtoGreaterTree.java

public class BSTtoGreaterTree {
	public static int sum = 0;
	public void greaterTree(Node root){
		if(root!=null){
			//visit the right node first
			greaterTree(root.right);
			//store the node value in temp
			int temp = root.data;
			//update the sum, sum till previous visited node
			root.data = sum;
			//update the sum for the next node
			sum = sum + temp;
			greaterTree(root.left);			
		}else return;
	}
	public void inorder(Node root){
		if(root!=null){
			inorder(root.left);
			System.out.print("  " + root.data);
			inorder(root.right);
		}
	}
	public static void main(String args[]){
		Node root = new Node(10);
		root.left = new Node(5);
		root.right = new Node(15);
		root.left.left = new Node(2);
		root.left.right = new Node(7);
		root.right.left = new Node(12);
		root.right.right = new Node(20	);

		BSTtoGreaterTree b = new BSTtoGreaterTree();
		b.inorder(root);
		System.out.println("");
		b.greaterTree(root);
		System.out.print("Greater Sum Tree: ");
		b.inorder(root);
		
	}
}

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