/*

    class Node
       int data;
       Node left;
       Node right;
   */
   void topView(Node root) {
      if (root == null) return;

      Stack<Node> stack = new Stack();
      while (root != null) {
          stack.push(root);
          root = root.left;
      }

      while (!stack.isEmpty()) {
          root = stack.pop();
          System.out.print(root.data + " ");
      }

      root = root.right;
      while (root != null) {
          System.out.print(root.data + " ");
          root = root.right;
      }
   }