ab wrote:That wasn't my question. I have a program I can use to solve it by brute force. My question was how did you generate the puzzle?
A search through the specific pattern resulted in 53 non-equivalent minimal 20s, plus a number of non-minimals. All 53 are 'hard' to solve (at least hard for 'Simple Sudoku' and also my solver). In the previous post the 'vert hardest' was chosen (one of two puzzles where the solvers could not fix any extra cells). Among the non-minimals were both 'easy' and 'hard' ones.
- Code: Select all
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# 48 M20s. Pattern: 0-9-6-0-0. Minimal puzzles with 20 clues, full symmetry.
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000000000010020030002405600004000500020000010006000200005607400030080020000000000
000000000010020030002405600004000500020000070006000300005603400070080010000000000
000000000010020030002405600004000500020000070006000800005906400030010090000000000
000000000010020030002405600004000500030000070006000800005602400070010020000000000
000000000010020030002405600004000500070000010006000700005608400090030070000000000
000000000010020030002405600004000500070000020006000700005608400080030010000000000
000000000010020030002405600004000500070000080006000300005602400020070010000000000
000000000010020030002405600004000500070000080006000300005602400080010020000000000
000000000010020030002405600004000500070000080006000700005601400080030090000000000
000000000010020030002405600004000500070000080006000700005603400020090010000000000
000000000010020030002405600004000500070000080006000700005609400080030090000000000
000000000010020030002405600004000500070000080006000900005602400080010020000000000
000000000010020030002405600004000700070000080006000500005608400020030010000000000
000000000010020030002405600006000700080000010007000400004706300020050080000000000
000000000010020030002405600006000700080000010007000400004706900020050080000000000
000000000010020030003405600004000300070000080006000500005602400030080010000000000
000000000010020030003405600004000300070000080006000500005602400080070010000000000
000000000010020030003405600004000500020000070006000800005608400080030010000000000
000000000010020030003405600004000500020000070006000800005609400070010090000000000
000000000010020030003405600004000500070000010006000300005602400030080070000000000
000000000010020030003405600004000500070000010006000800005602400030080070000000000
000000000010020030003405600004000500070000010006000800005602400030090070000000000
000000000010020030003405600004000500070000020006000700005608400080030010000000000
000000000010020030003405600004000500070000080006000400005608900080070010000000000
000000000010020030003405600004000500070000080006000700005206400090080010000000000
000000000010020030003405600004000500070000080006000700005601400080030010000000000
000000000010020030003405600004000500070000080006000700005602400080070010000000000
000000000010020030003405600004000500070000080006000700005806400080010020000000000
000000000010020030003405600004000500070000080006000900005609400090070010000000000
000000000010020030003405600004000500070000080006000900005806400080070010000000000
000000000010020030004105600005000100070000020006000400008406500030010090000000000
000000000010020030004105600005000100070000080006000400009406500080010070000000000
000000000010020030004105600005000400020000070006000800008206500070030010000000000
000000000010020030004105600005000700030000010008000400007406500080090020000000000
000000000010020030004105600005000700070000010006000400008604500090030020000000000
000000000010020030004105600005000700070000020006000400008406500090030010000000000
000000000010020030004105600005000700070000080006000400002406500080030010000000000
000000000010020030004105600005000700070000080006000400008406500030010020000000000
000000000010020030004105600005000700070000080006000400009604500080010020000000000
000000000010020030004105600005000700070000080006000400009604500080070020000000000
000000000010020030004105600006000400030000070007000500005604800090010020000000000
000000000010020030004105600006000400030000070008000500005604200070090010000000000
000000000010020030004105600006000400070000020008000500005704800030010090000000000
000000000010020030004105600006000400070000080008000500005604700020030090000000000
000000000010020030004105600006000500020000070008000400005204800070030010000000000
000000000010020030004506700003000500080000010007000400005407200090060080000000000
000000000010020030004506700003000500080000090006000400005402600090070080000000000
000000000010020030004506700003000500080000090007000400005407200090060080000000000
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Credit goes to ab for finding the first 20-clue puzzle in this pattern (as far as we know). Finding the first one is always most difficult. The search algorithm was not a complete search, it's based partly on input seed, and partly on random (- in effect a partial/limited search through the complete pattern). ab's 'first' puzzle (#08) was among the input seed, so it can be regarded as ancestor, or 'grandfather' to all (not 'father', since none of the minimals were 'first generation' results). The #01 ('almost similar' pattern) was also input to the process.
It's also possible more than these 53 were found. After a simple (incomplete) normalization process about 200 'different' puzzles were listed. But I could only separate with certainty the 53 listed above, so the rest are possible isomorphs.
[Edit: Five isomorphs taken out. Leaving the 48 non-equivalent puzzles.]