by denis_berthier » Thu Nov 07, 2024 11:37 am
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What's fun with Sudoku is, it always keeps surprises in store.
I computed the template-depths of puzzles with extreme numbers of clues (in the lower and upper ends).
Nothing special to say about the T values obtained: they span the T0 to T3 levels, as expected after my previously reported calculations for the controlled-bias collection.
But, if you consider the computation times, the results are quite noticeable:
- computations for the 17-clue puzzles (49,158, all in T&E(0 or 1) are slower than for the controlled-bias collection;
- most of the known puzzles with 39 clues (2,650, all in T&E(1)) are in T3 (23 in T1, 473 in T2, 2,154 in T3), but the computations are much faster than for T&E(1) to T&E(2) puzzles in a similar range of T values;
- most of the 1st 100,000 puzzles with 38 clues (almost all in T&E(1) with just a few in T&E(2)) are in T3 (77 in T0, 4,710 in T1, 23,058 in T2 and 72,155 in T3), but again the computations are much faster than for puzzles with a similar range of T values.
You'd say that all is well and works as should be expected! Slower [resp. faster] computations mean more [resp. fewer] templates being considered. Note that fewer [resp. more] clues implies (statistically) more [resp. fewer] candidates - which should leave more [resp. fewer] possibilities to place a template[1] or a template[k>1]. This seems to explain the above computation times.
On the other hand, the computations for the controlled-bias collection show that, in T&E(1), there's no correlation between the number of clues or candidates and the template-depth of a puzzle.
Informal conclusion: for puzzles in T&E(1) (the only ones of interest for a human solver - leaving aside special patterns), the template-depth is not correlated with the number of templates to consider during resolution.
(The latter number is not an intrinsic property of a puzzle: it depends on the search order. However, it provides some informal measure of the computational complexity of solving with templates - be it manually or with a program).
All this incites me to conclude that templates are of little interest in the human solving or in the formal analysis of puzzles. (They're also slower than DFS, so they're of no interest for fast solving.)
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