Connect Levels in a Binary Tree

Given a binary tree represented in level order with the keyword null indicating a missing node, your task is to connect all nodes at the same level using a next pointer. The next pointer of a node should be set to the node immediately to its right in the same level, and if there is no such node, it should be set as null.

After connecting the nodes, each level of the tree can be viewed as a singly linked list with nodes connected from left to right. You are required to output each level of the tree as a single line in which the values of the nodes are concatenated with a -> arrow.

For example, consider the following two binary trees:

• Example 1

          1
         / \
        2   3
       / \ / \
      4  5 6  7
      

  Output:

  1
  2->3
  4->5->6->7
      

• Example 2

         10
         / \
        5   20
       /      \
      3        30
      

  Output:

  10
  5->20
  3->30
      

Note: The input is guaranteed to represent a valid binary tree in level order.

inputFormat

The input is given as a single line containing space-separated tokens representing the binary tree in level order. Each token is either an integer or the string null, which signifies a missing node.

For example:

1 2 3 4 5 6 7

outputFormat

Output the connected node values level by level. For each level, print the node values connected by the arrow -> without any extra labels. Each level should be printed on a new line.

For the above example, the output should be:

1
2->3
4->5->6->7

## sample

1 2 3 4 5 6 7

1
2->3
4->5->6->7

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