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Dijkstra's algorithm

1. Original procedure of the algorithm

2. Proposals of adaptation

3. Discussion of pros and cons

It is clear the first method is advantageous to teachers. The graph is well arranged and understandable, all the nodes and edges are in one place. Nevertheless, blind students do not find the method good. Performing the algorithm is not effective because of the frequent movement between rows and columns of one sheet of the table.

The second method eliminates the disadvantage. When switching from one sheet to another the cursor remains in the same position as it was previously and therefore a user gets all the processed data immediately without searching for them for a long time. Furthermore, the second method is more economical concerning memory requirements. When switching between the two sheets the student needs to hold only the tentative distance of the current node from the initial one n his/her memory. All the other data s/he needs (the weight of the edge and the successor's identification or its current tentative distance from the initial node) are easily and quickly accessible. One of the blind students came with an interesting proposal of improvement: "I could change the name of the sheet and put there the information about currently processed node. I have it on my refreshable braille display all the time I work with the sheet, therefore I need not keep it in my memory." We also recommend teachers to provide students with a spreadsheet file containing two sheets only, one for reading the graph, the second for editing labels of the nodes. Otherwise blind users may switch (by mistake) to the other sheet with irrelevant data and can become confused easily.

The third method respects the spatial arrangement of the graph preferred by sighted users of the algorithm and blind ones assessed it as the best one too. "I prefer working with a tactile version of the graph. One gets a better idea of the relationships between nodes. When working with the graph in a table, nodes are arranged alphabetically even though they need not be neighbours," said one of the visually impaired students of our university. All the experienced blind users came up independently with a proposal to write nodes on one line of a plain text editor instead of separating them, each node on one line, which was recommended first. As they have a refreshable braille display they can immediately observe all the (un)visited nodes. However, the third method presumes students with the knowledge of Braille and their ability to work with tactile materials.