Write a method called numberNodes that changes the data stored in a binary tree, assigning sequential integers starting with 1 to each node so that a preorder traversal will produce the numbers in order ( 1, 2, 3, etc.). For example, if a variable t refers to reference tree #1, the call of t.numberNodes(); would overwrite the existing data, assigning values from 1 to 6 to the nodes so that a preorder traversal of the tree would produce 1, 2, 3, 4, 5, 6 as shown in the following diagram. Do not change the structure of the tree, only the values stored in the data fields. Your method should return the number of nodes in the tree.

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2 4 6.