How is the complexity figure calculated?
It is the number of times the thread had to be unwound in order to iterate through all possible puzzle solutions. The figure is, of course, strategy-dependent. A measure of a good strategy is that it leads to a low complexity figure. ‘Fiendish’ puzzles tend to have a complexity figure of 150 according to the Least Candidates Hybrid strategy, whereas the 20 and 21 cell puzzles might have complexity figures of around 500. The FirstAvailable strategy will often assign a complexity figure in excess of 100000 to such puzzles. I’ve noticed that the Random Least Candidates Hybrid strategy tends to return (as it’s random, it often returns a slightly different complexity figure each time it’s evaluated) a lower complexity figure that the Least Candidates Hybrid strategy. I’m not sure exactly why this should be and I intend to investigate the matter. I think it’s because, when all things are equal, Least Candidates Hybrid will tend to work at the top-left hand corner of the grid, while Random Le
