good resource links

https://support.office.com/en-gb/article/Power-Pivot-Add-in-a9c2c6e2-cc49-4976-a7d7-40896795d045

http://stackoverflow.com/questions/127704/algorithm-to-return-all-combinations-of-k-elements-from-n

http://www3.cs.stonybrook.edu/~skiena/combinatorica/animations/dijkstra.html

https://www.cs.auckland.ac.nz/software/AlgAnim/dij-op.html

http://www.pythontutor.com/visualize.html#mode=edit

http://www.contextures.com/xladvfilter01.html