adds script for binary trees

Author: kyleshevlin

trees/binaryTreeScript.md

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+# Binary Trees and Tree Traversal
+
+Binary trees are trees whose nodes can only have up to two children, hence binary. We store this data as the left and right of a node.
+
+We'll use a function to create our binary node object. a binary node receives a key as an argument, has a left and right property set to null, as well as methods to addLeft and addRight.
+
+addLeft and addRight receive a key, create a new node, update left and right respectively, and then return the new node.
+
+Now we can create our binaryTree factory function. Since trees must have a root, our function receives a rootKey as an argument. We can then create the root node using our node factory function. We pass this to the object we return from the function.
+
+Binary trees have three specific types of traversals: in order, pre order and post order. Let's create a traversals enum. Each item in our enum will be named after the type of traversal it is. The value of each will be a function that we can use when traversing our tree.
+
+In order traversal always visits the left branch, then our current node, follwed by the right branch. Since these traversal functions are called recursively, we need to guard against a node that is null. So if the node is not null, we call our traversal down the left branch, then visit our current node, then traverse down the right branch.
+
+Pre order traversal is very similar, but we change the order so that we visit our current node first, then followed by the left branch, then the right branch.
+
+Post order traversal visits the left and right branches before visiting the current node.
+
+Now, let's add a print method to our tree that accepts an orderType as an argument. The default will be inorder, as that's the most common traversal.
+
+We'll keep our print function simple. As we visit each node, we'll add the key to the result and return a string. Using our enum, we can trigger the correct method call to start our traversal.
+
+Let's create a simple binary tree, I have one to copy paste in here, We can call print on it several times and compare the results.