a_161_TransForm_Sum.java

public class a_161_TransForm_Sum {

    static class Node{
        int data ;
        Node left , right ;

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

    public static int transform(Node root) {
        if(root == null){
            return 0 ;
        }

        int leftChild = transform(root.left) ;
        int rightChild = transform(root.right) ;

        int data = root.data ;

        int newLeft = root.left == null ? 0 : root.left.data ;
        int newRight = root.right == null ? 0 : root.right.data ;
        
        root.data = newLeft + leftChild + newRight + rightChild ;

        return data ;
    }

    public static void preorder(Node root){
        if(root == null){
            return ;
        }

        System.out.print(root.data + " ");
        preorder(root.left);
        preorder(root.right);

    }


    public static void main(String[] args) {
           /* 
                        1
                      /   \
                     2     3
                    / \   / \ 
                   4   5 6   7
         
         */

         Node root = new Node(1) ;
         root.left = new Node(2) ;
         root.right = new Node(3) ;
         root.left.left = new Node(4) ;
         root.left.right = new Node(5) ;
         root.right.left = new Node(6) ;
         root.right.right = new Node(7) ;

         transform(root) ;
         preorder(root);

    }
}