[rules-users] Why is solving a partial puzzle much slower than generating one from scratch?

[aitchnyu]

Sorry if I called it by a misleading name (3x3) . It means a regular sudoku
like http://www.sudoku-solutions.com/ .

And I hacked on NQueens to make it. Only the row is the planning entity.
Each digit has a value, row, column and a fixed status. A fixed digit has
row, column and value assigned and fixed status set to true (you must not
reassign row of this). An unsolved digit has a null row, with column and
value assigned and fixed status set to false.

I included three cases. It solves a completely blank grid, it doesnt solve a
24-digit problem (it gets stuck at a step, see included log snippet), it
solves an easier 8-digit version of same problem in *much longer time*.

*Case*: Output of solving a completely blank grid
12:42:33.977 [main] INFO  o.d.p.c.l.DefaultLocalSearchSolverPhase - Phase
local search finished: step total (148), time spend (5491), best score (0).
12:42:33.977 [main] INFO  o.d.p.core.solver.DefaultSolver - Solved: time
spend (5491), best score (0), average calculate count per second (17598).
 
*Case*: solving problem 1: 24 digits of
http://puzzles.about.com/library/sudoku/blprsudokux01.htm 
12:51:34.279 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (10530), time spend (164914), score (-3),     best score (-3),
accepted move size (456) for picked step (Digit:4 (Row 5,Column 2) block
code[10]  => Row 3)

It gets *stuck* here forever.
12:59:31.398 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4265), time spend (74003), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 5,Column 7) block code[12]  =>
Row 3).
12:59:31.429 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4266), time spend (74034), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 3,Column 4) block code[11]  =>
Row 5).
12:59:31.444 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4267), time spend (74049), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 5,Column 4) block code[11]  =>
Row 3).
12:59:31.459 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4268), time spend (74064), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 3,Column 7) block code[12]  =>
Row 5).
12:59:31.474 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4269), time spend (74079), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 5,Column 7) block code[12]  =>
Row 3).
12:59:31.493 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4270), time spend (74098), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 3,Column 4) block code[11]  =>
Row 5).
12:59:31.508 [main] DEBUG o.d.p.c.l.DefaultLocalSearchSolverPhase -     Step
index (4271), time spend (74113), score (-3),     best score (-3), accepted
move size (520) for picked step (Digit:7 (Row 5,Column 4) block code[11]  =>
Row 3).


*Case*: reducing predefined digits down to 6
13:02:31.093 [main] INFO  o.d.p.c.l.DefaultLocalSearchSolverPhase - Phase
local search finished: step total (554), time spend (12849), best score (0).
13:02:31.094 [main] INFO  o.d.p.core.solver.DefaultSolver - Solved: time
spend (12850), best score (0), average calculate count per second (25229)


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