Sudoku no 686 (Extreme)

This puzzle has a Hodoku grade of 18788.

Andrew Stuart's solver was unable to grade it.

Sudoku grader and solver 

See answer

Sudoku no 665 (Diabolical)

This puzzle has a Hodoku grade of Hard (1376) so it would have qualified for inclusion in my book as all the puzzles there have a Hodoku grade between Hard (1000) and Hard (1999).

Andrew Stuart gives it a grade of 201 (Very Hard) on his main page but calls it Diabolical when you look at the solve path.

Please click here if you would like to see my book. Amazon shows you the first 18 puzzles in the preview.

Solve online

Sudoku grader and solver

See answer

121 Extreme Sudoku Puzzles

Some time ago, I ran my sudoku creation program 10,000 times with the idea of creating enough extreme puzzles to fill a book which I could sell on Amazon and elsewhere. I intended to format the puzzles in Andrew Stuart's grader and solver, copy them into a Google Doc and save it as a PDF, which I could then turn into a paperback.

I soon realised that this was going to take longer than expected and gave it up as a bad job. I am now working on a computer application which will create the book for me.

The puzzles I created are therefore surplus to requirements so I have pasted them below. Each one shows its Hodoku grade and you will notice that I have only included puzzles with a grade over 5000.

The puzzles were created before I amended my C program to avoid occasional pattern repetition as explained here. However, this should not be a problem as this is present in all the commercially available puzzles I have ever seen. I seem to be the only person bothered by it:

000003000095800006006540000120000030500300008000070040000000071004000600380000009 #1 Extreme (5102)
200054086005060000000000030070010600000006010000900042401000007000800490007009000 #1 Extreme (5574)
000807000702005001090000400009000300070900006000200590807050000400030000000080250 #1 Extreme (5518)
030104000065020004200007500040600000500000006000008049670000010000200703902000000 #1 Extreme (5054)
800090000300502000000000007600000030000001072520030960003010009005400000000280010 #1 Extreme (5018)
000904006030000084060800300050070000910008000006105008000059230000000009700200060 #1 Extreme (5946)
003900100000060407400002000000034600020100050000000080602301908000000700010000003 #1 Extreme (5338)
000003000239000000700806090000308620000260070000005409008000000400070800097000040 #1 Extreme (5620)
010020000408000003050700008000000015030000000800019040000002000005000006600094070 #1 Extreme (5436)
800740020007000000040005030904000061073000080080600700009206000000100500460000000 #1 Extreme (5000)
007060029000000000050290048700001000006050090080000000002080001000075380300900000 #1 Extreme (5574)
690000800000608070000040000000000001009301000700205000080000200030500700040980060 #1 Extreme (5592)
000000900700000041000821000007000000280100039000004008030500000004060390502090010 #1 Extreme (5504)
000900003972600100000005200700006000091040000800000010607208050005000072030500000 #1 Extreme (5470)
000130000005006004390007000023000700514700600000000002900080010000300060008000239 #1 Extreme (5990)
000904008070000000600310500400000070027800010106040002000030000000150400009006080 #1 Extreme (5034)
000040065800000100005701000300079014610003700004000000720008900000004000000010020 #1 Extreme (5204)
090102005054030000002049800200050000000807010010300600046000900580000140000000006 #1 Extreme (5218)
060000004820000700300806000002004000000200090050080100400000008603907000000100300 #1 Extreme (5448)
107200600080030000000104000509041002300009040002000007003400090000006020000500006 #1 Extreme (5584)
018000007072000063300000000030002040007030600100004700001800900400000500080070000 #1 Extreme (5204)
000070600000500700400060085004000300050300819830001000701000040006180000500002000 #1 Extreme (5710)
300080010010900700000240006540006000091002000200000040005800401009000270004300060 #1 Extreme (5626)
009020034054010020000600070016000000020460000500007000090000000000005010800390200 #1 Extreme (5988)
000080000009103040000000603060500700000097000000040008170900300800000090400070002 #1 Extreme (5542)
002006000100004000059100230000020500000000080320000000090080005010009300700300906 #1 Extreme (5198)
607800000020700003003000001900020080000960007400000900700000090204050100000001500 #1 Extreme (5814)
000000600000085010000012900107000009000000030009007082302000067500400000040009000 #1 Extreme (5692)
000800120080006000350070000070900004200008090030100702000000930023040000000080007 #1 Extreme (5734)
000100503100905000000280006290500600000007000300010002030800000006000020008000370 #1 Extreme (5108)
000082300030007000001000080008401006000000900006200010007800605000053702090000000 #1 Extreme (5138)
006000501047000000000000490400089120261004000000000040008700000910048070000902000 #1 Extreme (5130)
010050000030000607046008900001040000052071003000300000500010048000000000000002790 #1 Extreme (5158)
300020040000040093006000800900130560000000000500000007080000600402006010001800000 #1 Extreme (5490)
001090000000000002309201080040100000050340200100008007000002308005000000807400105 #1 Extreme (5080)
040050100000300020900006000020008090001207050300160000007004800059000407000000060 #1 Extreme (5274)
060000170030500400700009305000903000270010004001000700000400900840000060000000003 #1 Extreme (5368)
000300000302060007006002530700000094009000000050003600007041000400080306080000700 #1 Extreme (5870)
300200009800501700001000040020045000000900000047800003709000300000003000000000617 #1 Extreme (5950)
009000300000000090026003005000000000000009572100720030005000040060087000703602000 #1 Extreme (5408)
008060502100000008000000430504301009030500040970008000005800000400906380000200700 #1 Extreme (5294)
005302000070040000001007920000425007000039001000000050708000003034000060090050800 #1 Extreme (5930)
040000001003005098520000000008470000000000580000300006007000000200009700000100034 #1 Extreme (5136)
000302700038046000000010000076104000003000000000000904000000002800020090004580013 #1 Extreme (5118)
000005080000300006069040000900000450003060700080003090104830000000700000300000020 #1 Extreme (5502)
600730010003000760000002000009173000305900000007000400500010006200040900090020030 #1 Extreme (5280)
000000050048000600103050000900024536200080004000009070020900160000600700009075000 #1 Extreme (5316)
006000400802003100005700063050004030000080090200005000008010004600000000401200000 #1 Extreme (5388)
000000300019062000000900010020000800405120600000000070000000004082037050003001000 #1 Extreme (5012)
000038000000050000000000709078009000620004000040080050760000004000016200002300100 #1 Extreme (5538)
010520000020006007600000201003200000004000000500130090900000030000078600000000084 #1 Extreme (5132)
005104090070000500004080006420600000003000001000900028000090050600350002030700000 #1 Extreme (6920)
700080000030670804001050020000000200906000040000800593000040000040003001600100080 #1 Extreme (6270)
000030080008000700000400096037002600005007048060100000000900000040210000000000137 #1 Extreme (6074)
830040000007080109001700300012000000008600004600000050000107400000004203003000010 #1 Extreme (6996)
000030000007005008800090200000607000045000002000200300000001730009000000004300060 #1 Extreme (6970)
004000000070002006010007900050000201000503000090000000003008040100090008008040503 #1 Extreme (6152)
000800400070034020006507008300019000020000080007000004060005003089000060010000500 #1 Extreme (6394)
006090080900000300010007020009100000570903000068020000000400800005000042100030056 #1 Extreme (6626)
000100907504020800008000004200000040000000300000570090000030000402600530100409060 #1 Extreme (6036)
005601900600004000000050200206000030030020010109403000000000620300500004000009007 #1 Extreme (6434)
200007000009000004100300080060000002007400638000009100006008000501000000003605420 #1 Extreme (6696)
100900000008040000090200001080000009000700500200030860001000020004076000003010480 #1 Extreme (6028)
700006902002007000900300760509700001040000090300000200000400008005090000604102000 #1 Extreme (6120)
008040030904200000000070000760009100000016020500300400005000000010090700800000092 #1 Extreme (6028)
960100000500304000300809001000000082003000000100905700200048039004500107000000000 #1 Extreme (6616)
030006002050800000609004000472000000000000063000090200005030900000008300180000640 #1 Extreme (6878)
070000000060200900009780100200070804014000000008600030040030000050000067000100000 #1 Extreme (6482)
300007005000639000060005904020003070000000000801020006400070500600800010000000008 #1 Extreme (6782)
096700010070000005800400700002004000701000000000601087000090030300140800060803000 #1 Extreme (6100)
029003000408000069000000800002700000800005000105062094000006050706020900200300680 #1 Extreme (6192)
000000402008107009092008000400000000007800004050600030100003028000009700030000100 #1 Extreme (6104)
000490006000010000040002075010600500034000008060040030370020061000800000200070300 #1 Extreme (6056)
000300701090002004000060000008053010010000900600000308140500027900000000502004009 #1 Extreme (6390)
010000000205080000300004126000300002800007400060900000001000500009010048400000009 #1 Extreme (6550)
006040000500600180030002050000230005700000008000109200000065830000000000605000091 #1 Extreme (6024)
000058092900000700040070030060007000070020500002100004306000000091003080000902000 #1 Extreme (6610)
000000020040000730010030406005000803037006000900040000090204000000380050803000001 #1 Extreme (6320)
071000002009170040050006000000002000010400900005000083080047005900520004000601700 #1 Extreme (6282)
600005000000000080201800007004000900500200608000009004010508000062091000003002400 #1 Extreme (6274)
410000009060100002009067000095000000000009070103080500300000000080500210000070400 #1 Extreme (6224)
052400093009000800310007000007085000500100000000270008090540000030000025670000040 #1 Extreme (6238)
080004020000000040300060009000000200005020003040009000006030000070600090010002800 #1 Extreme (6290)
500060090003040006080002000007000004100030000000906010000810230020000058050000007 #1 Extreme (6448)
000080000470020806300100020060000090205000400007900001040000008500006002000010630 #1 Extreme (6324)
001460000080200600200000050048030060503000100000000005002000010030071008070500000 #1 Extreme (6528)
000401500064005000003082000600510070000000090080000006050020609409008000200000100 #1 Extreme (6364)
000680705500000420000000000600010308004002000091000070008009000900350000070040001 #1 Extreme (7078)
050410006100670000000009000200800400005040730000500001408000000001794800370000600 #1 Extreme (7372)
000000062005009010000000903006350000004070051030200008070000495300000000000010000 #1 Extreme (7692)
203000500090000027005040000010092008000000060400805000080706000002300000900000200 #1 Extreme (7348)
100005000000001400003040012000000086000070930060000000340028050600590000800000700 #1 Extreme (7238)
400010070065000000100000008029070000000058000007020040700001060040006003080000102 #1 Extreme (7714)
000900027100002000080000001050060208060083040700000060009140000000008500006000070 #1 Extreme (7396)
400070006007650034050000000028700000060000803000009000000100080240030010806400000 #1 Extreme (7024)
029000000400690000006008200010039050000100094000000810001900030780000000000005060 #1 Extreme (7388)
000000710003700060840003900008009005300000084000060000500006000010200040002900000 #1 Extreme (7342)
009000000400230000083500071000000000030000407000070205940006020000802000060000150 #1 Extreme (7504)
090000076008000009002000000000040805470000090000600010610500300800720000040001000 #1 Extreme (7344)
004005008001079000600010700900000006000032000083900100000050602400100079007000080 #1 Extreme (7172)
000103700007009050060000089050600000900051204002000005003000921090004000700000000 #1 Extreme (7324)
030400090000000053140060008007200000900040060010009000061000005005103200000000900 #1 Extreme (7740)
500100000090003000200097400600008031000200000080010020730005900010000008008000000 #1 Extreme (7578)
050070030609020500004008000200080700003001005008000060300060000000000617400200800 #1 Extreme (7624)
034000000160040000800200300000036008000500000090017000000005000040900680500000072 #1 Extreme (7042)
000004010050170000000800002000000380800635000600400700001000030090301804080090000 #1 Extreme (7008)
010408000000700150000000070000130006800020000200005037040000001093000060620000800 #1 Extreme (7720)
000035000071900000000002300000100400080000000009080500005000140130000680408000903 #1 Extreme (7514)
030600000401002006080740000062000007900010000800527000000000650300000109004060002 #1 Extreme (7150)
000000760005800002200000900008074000309050080040030000050600000700090010030000400 #1 Extreme (7928)
410700005005960800000000020040091003800050009007000000080000060123500900000020000 #1 Extreme (8610)
030010900081002600200500300106400000000000030000690470017000000009000060000100800 #1 Extreme (8594)
005020030700000000100680020004390002800000006001000400000050090000009800008064007 #1 Extreme (8288)
000046000571090000000000039050800070080060000300007000000002703124000050000050400 #1 Extreme (8420)
090007604000000000700000390004300000009005070050800030200000050008006001600400000 #1 Extreme (8304)
000008900003004600070600034300020009500400060000703000609300007100000000080009040 #1 Extreme (9722)
000010007930020000000000650857460020000000700020801000400500003200000080060000470 #1 Extreme (9840)
000000003200001500017020004400093001050000000600050300008275000000000000020040600 #1 Extreme (9188)
940000000001000002008504300600200090000006001000000700090300005106070800470000000 #1 Extreme (12668)
000010020000007000008500907030060500001000060400005802000000096750300000020004700 #1 Extreme (13280)
000000400620000000003007910005091000970020000000800030700009006000005090000180004 #1 Extreme (18516)

Sudoku no 626 (Diabolical)

I have recently been discussing the creation and grading of sudoku puzzles with a member of my Sudoku Puzzles Facebook group.

I make my own puzzles using a C program, which I wrote myself in 2012. This creates a valid solution then randomly removes as many clues as possible, whilst still retaining exactly one answer. I then grade each puzzle using Hodoku and/or Andrew Stuart's grader and solver (see link below puzzle).

I find that this method produces puzzles with a range of difficulties from easy through to extreme. None of my puzzles have any surplus digits.

The member mentioned above asked me to grade three puzzles for him so I submitted the first one to Andrew Stuart's grader and solver (see link below puzzle), which said it was very easy. It also had several spare digits i.e. clues which could be removed to leave a slightly more difficult puzzle, which still had exactly one solution. I have seen this from time to time in sudoku books but personally I don't like it.

I removed as many of the spare digits as possible, which created the diabolical puzzle below:

Solve online 

Andrew Stuart's grader and solver 

See answer 

Sudoku no 618 (Easy / Moderate)

Hodoku says this sudoku puzzle is easy. Andrew Stuart's grader and solver says it is moderate:

As an Amazon Associate I earn from qualifying purchases:

Solve online

Sudoku grader and solver

See answer 

Sudoku no 487 (Extreme)

Andrew Stuart's site graded this puzzle as Extreme / 1267.
Hodoku gave it a grade of Extreme / 8560:

Sudoku grader and solver 

See answer

Sudoku no 486 (Extreme)

Andrews Stuart's site graded this sudoku puzzle as Extreme / 612.
Hodoku gave it a grade of Extreme / 5564:

Sudoku grader and solver 

See answer

Sudoku no 485 (Diabolical)

Andrew Stuart's site graded this sudoku puzzle as Diabolical / 276.
Hodoku gave it a grade of Extreme / 1994:
 

Sudoku grader and solver

See answer

Sudoku no 484 (Tough)

Andrew Stuart's site graded this sudoku puzzle as Tough / 83.
Hodoku gave it a grade of Unfair / 1058:

Sudoku grader and solver

See answer

Sudoku no 483 (Moderate)

Andrew Stuart's site graded this sudoku puzzle as Moderate / 75.
Hodoku gave it a grade of Medium / 398:

Sudoku grader and solver 

See answer