Tricky puzzles to solve
Difficult to solve puzzlesList of contributions in 'Difficult Puzzle'
| Difficult Puzzle contributed by SudokuDragon |
| There does not seem any place to allocate. Has anyone any suggestions on how best to tackle this one?  Click here to download this puzzle
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| Submit477 (re: Difficult Puzzle) contributed by Rob Puzzle |
| You are right there is no easy square to solve. There is only one 2 allocated anywhere, and only two 4s and 7s. To get you started try this strategy. Concentrate on region Aa and Row C. A 3 must either be in Ac or Ca and a 9 in Ca or Cb. But 2 can only occur Ca or Cb in this region so this means a twin has been found and 3 can not occur in Ca it must be in Ac. That should unlock things a fair bit.
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| Agree (re: Submit477) contributed by Lynne |
| I agree that is the best way. But you don't say why you chose it in the first place. How I'd approach it is to flick through using the possibilities bar in SudokuDragon. Go through all the numbers 1 to 9 using the ALT+number keyboard shortcut. You'll see all 1s and 5s are allocated and that 6,8 and 9 all have a very symmetric pattern (often tricky to solve). There are lots of places that 2,4 and 7 can be allocated - far too many to think through easily. The only remaining number 3 has relatively few squares and a non-symmetric pattern. That is why I'd home in on looking at where 3s could be allocated.
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| Steady Progress (re: Difficult Puzzle) contributed by Rob Puzzle |
| After putting the 3 in Ac you can now put 4 in Ah. Then in region Bg the square Bi can only take one value a 2. Now have lots of twins that aren't helpful and it is the 3s that are worth loking at. In row H there is only one place a 3 can go Hg and in region Ga the 3 must go in Ia. That then forces a 3 in Gd and a 3 in Ch and the last 3 in Di. That is all the 3s allocated. Putting a 7 in Cg completes the region and that 7 forces a 7 in Gi. With only 25 squares left to solve that's probably solved it more or less.  Download this puzzle Click here to download this puzzle
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| Submit2234 (re: Difficult Puzzle) contributed by Hamish McW |
Sort of Swordfish with 5 in Bb Hf Download this puzzle Click here to download this puzzle
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| Challenging Progress (re: Submit2234) contributed by Alexander |
| Yes, I agree you haven't overlooked anything too easy. I can't see anything forced by the only choice; only square; subgroup exclusion or twin exclusion sudoku strategies. Always useful at this stage to look through the possibilities one by one using the possibility bar. In this case it is the '5's that are helpful. In row F there are only two options Fb or Fh. If it was Fb then that has knock on effects, in row H the 5 would have to be in Hc but in area Da the only square left would be Dc. So putting 5 in Fb would require a 5 in the same column c for Dc and Hc. This can not be right - the 5 must go in Fh - no other choice. If you do that sudoku assignment the rest follows fairly easily I think.
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| Question to Alexander (2595) (re: Challenging Progress) contributed by CBK |
| Hello, You said, about the puzzle < When you talk about the two options for the 5s in F, I see you. When you say 5 in Fb, the 5 in the H row is Hc, I see that. But when you bring up the Da box(area), and say that 'the only square left would be Dc', I don't follow you. I assumed you are saying that the only square left for a 5 is Dc, but didn't you already a 5 in the Da box/area? Why talk about a second 5 in the Da box? The 5 has already been placed slot Fb at the beginning for the Da box/area. Obviously if you were to place a second 5 in that box, it would have to in Dc and would be in conflict with the 5 in Hc. But that is two 5s in the same box Fb and Dc!?! I did a check on that option, it is works, out, but I obviously don't understand the logic. Could I get some help? CBK
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| Submit2608 (re: Question to Alexander (2595)) contributed by Alexander |
| Sorry, yes I was wrong, not sure what I was thinking. I still think the correct strategy was to choose between Fb and Fh for where to place a 5. If you choose Fb you can prove this is incorrect - but by a longer chain than I thought - however all the steps are straightforward 'forced' choices (only place or only square). First look at column c. 9 must go in Dc; 4 in Gc; 6 in Ec; 7 in Cc and 5 in Hc to complete the column. Now complete row C with 6 in Cb and 1 in Cg. Now go to column g with 9 in Bg and 4 in Eg and 7 in Ig. It now gets to the crunch in column b. 1 must go in Ib but this forces an impossible allocation of 3 - it must go in BOTH Bb abd Db. This means the initial Fb choice was wrong - it must be the other alternative. There's probably a better way of proving this but I can't see one. Apologies again.
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| Beware! Very Challenging Puzzle from Sudoku book, please help (re: Difficult Puzzle) contributed by CBK |
| I got through 77 Sudoku puzzles in 'The Ultimate Sudoku Challenge' and hit one in the Section called 'Beware! Very Challenging' and I got stuck. I included it (I think). Can anybody just get the next possible slot? and tell me how? I checked all my slots so far, and the programs says they are ok. Thanks CBK  Download this puzzle Click here to download this puzzle
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| Submit2620 (re: Beware! Very Challenging Puzzle from Sudoku book, please help) contributed by Hamish McW |
| I believe you are right this is a tricky one. I can't see any way but to use trial and error. Fortunately both the '1's and '2's have very limited possibilities - there is only one correct and one incorrect allocation possible. So I think all you need to do is to try allocating 1 in Db or Dc and follow the logic through. It will either solve or lead to a contradiction. This probably makes it a 'bad' puzzle (see the discussion on Labyrinth) so don't be too hard on yourself.
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| Solution, 4 months after I gots stuck, and no guessing (2702) (re: Beware! Very Challenging Puzzle from Sudoku book, please help) contributed by CBK |
| Hello, Well I solved it. Like I said in title, I got stuck a long time ago, and just decided to try again after many failures. The Sudoku Dragon program actually helped me, because I found a new strategy from one of its randomly created puzzles. I will detail the solution here. Unfortunately I don't know how to get puzzles to appear here with those nice labels for row and Column, but I will use that system anyway. The Key item is the three squares Eb, Ec, and Ed. If you look at those squares, there are only 3 possible choices 5,7,9. Even though 5, 7, 9 appear in the other possible slots for row E, the fact that those 3 are limited to three slots is important. For example, if you try to determine if a 5, 7, or 9 could be a possible solution to any slot other that Eb, Ec, and Ed you will get a contraction. So if Ei were 5, then Eb could not be 5 and would have to be 9, but that would make Ec 7, and then the only possible options for Ed would be a 9 or 7, which obviously have been taken up already. Same for 7,9. This means that you can remove the options 5,7,9 from All E's other than Eb,Ec,Ed. This leaves another interesting thing, because now Eg can only be 4 or 6. If you look down g column you see that Gg can also only be 4 or 6. This means that you can remove 4 and 6 from all other squares in the g column, because 4,6 are limited to these to slots. So if you remove 4,6 from column g, the three slots Ag,Bg,Cg in the Ga box now have the same property like Eb,Ec,Ed. There are three options 3,7,8 in three slots where if you were to place any of them else in the box there would be a contraction or impossible slot. So 3,7 can be removed from rest of the box, the 8 was stuck in g already. Now this can puzzle can be solved. Whew! CBK
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| darn puzzle! (1243) (re: Difficult Puzzle) contributed by Jane D Doe |
just can't get any further... (sent to me by a friend) Download this puzzle Click here to download this puzzle
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