adding md on tree sort algorithm workshop

content/activities/tree_sort_algorithm.md

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+Title: Performing the tree sort algorithm
+Date: 18-11-2021
+
+![A visualization of the binary search tree, the tree is constructed with the definition of the tree sort as found on Wikipedia](tree-sort.svg)
+
+Repository for the workshop on the  [tree sort algorithm](https://en.wikipedia.org/wiki/Tree_sort).
+
+You'll find the workshop material in the `workshop` folder.
+
+## Recipes
+
+Recipes used during the workshop to execute the tree sort algorithm manually (with a group of people).
+
+### To insert a node within a tree
+
+*This recipe inserts a new node into an (empty) tree. It is assumed there is a place defined where the tree will be started (rooting point?). When the recipe is executed the **current position** is considered to be rooting point.*
+
+1. Look at your *current position*, if it's empty (there is no node) this will be your place: you are inserted in the tree, and the recipe is finished. If there is a node continue with step two.
+
+2. Ask the node in the *current position* for its value.
+
+3. Compare the answer of the node to your own value. Is your value smaller than theirs? Then follow the left arm of the node, and take that as the new *current position* and move back to step one. Otherwise continue with step four.
+
+4. Is your own value the same as or bigger than the answer the node gave? Then follow the right arm of the node, and take that as your new *current position* and go back to step one.
+
+
+### To measure the depth of a tree
+
+*This recipe discovers the depth of the deepest branch in the (sub)tree. It is initiated by asking the root or any other node to measure its depth.*
+
+1. Ask the node attached to your left arm for its depth, or take zero if you have none.
+
+2. Ask the node attached to your right arm for its depth, or take zero if you have none.
+
+3. Pick the greater one out of the answers you collected in step one and two, and add 1 (increment by one).
+
+4. Answer the number you calculated in step 3 to the node which asked you to measure your depth.
+
+
+### To traverse the tree in order:
+
+*This recipe transforms the (sub)tree into an orderd row (or list)*. It is initiated by asking the root or any other node to traverse.
+
+1. If you have a left node: ask it to traverse. Once it has finished traversing ask the resulting row (list) to stand to  the *left* of you. It is important the row maintains it order.
+
+2. If you have a right node: ask it to traverse. Once it has finished traversing ask the resulting row (list) to stand to  the *right* of you. It is important the row maintains it order.
+
+3. By combining the row on the left, yourself, and the row to your right a new row has formed. Tell the node who asked you to traverse that you're ready.
+
+
+## Code implementations
+
+In the folder `workshop/code` a simple implementation of the tree sort algorithm can be found.
+
+### workshop/code/treesort.py
+
+Implementation of the binary search tree. When the script is
+
+```
+python workshop/code/treesort.py
+```
+
+### workshop/code/tree-visualizer.py
+
+Visualizes a tree using graphviz
+
+```
+python workshop/code/tree_visualizer.py
+```
+
+### workshop/code/text-tree.py
+
+Reads a text (`workshop/text-to-sort.txt`) and generates a visual tree:
+
+```
+python workshop/code/text_tree.py
+```
+
+## Requirements
+
+The implementations are written in python and require python 3, find information on how to [install python here](https://www.python.org/downloads/)
+
+The visualizer and the text_tree both use graphviz to generate the visualization. Find information on how to [install graphviz here](https://graphviz.org/download/)
+
+The visualizer and the text_tree also require graphviz the [graphviz python bindings](https://pypi.org/project/graphviz). The easiest way to install them is through pip:
+
+```
+pip3 install graphviz
+```