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Str8ts StrategiesFrom syndicatedpuzzles.com, the puzzle solver's site |
Most of the Str8ts puzzle is about identifying the next cells that can be deduced from the clues in the black and white cells. On the easier puzzles this can be eye-balled - that is by scanning the rows, columns and the 'compartments' you should be able to find several opportunities to solve a cell. On the harder puzzles you might need to make notes in some cells to remind you of the the options. Both the Str8ts Player and the Str8ts Solver have the ability to type in small number notes. In the solver these are always displayed but they can be edited as well. For the purposes of outlining the strategies for Str8ts I am going to follow the list on the solver. Solving Sequence Start solving a Str8ts by working the smaller compartments ( 1, 2, 3 or 4 spaces) first. Using all the rules and clues and strategies listed below, the smaller compartments are simply easier to solve. Once solved, these smaller compartments start to fill in portions of the longer straights, and the filled in numbers remove themselves in rows and columns as possible numbers from the larger straights. By adding additional numbers to the puzzle we essentially are turning larger straights ( 5, 6, 7, 8 and 9 spaces ) back into manageable compartments that will be easier to solve. Especially if the following hands on strategies are used. Compartment Check |
This is the meat of Str8ts. A compartment is a set of white cells in a row or column bounded by the edge of the puzzle or a black cell. They will be between two and nine cells long. We know from the rules that all the numbers in a compartment must be a 'straight' - no gaps in other words - but the order will be unknown until you complete the straight. Given four cells with 5x8x, as in the example, we can know that to fill the gap we must use 6 and 7. If you are making notes or using the solver you can immediately eliminate 1,2,3,4 and 9 from those cells since they can never reach the clues we know about. Fortunately we have another clue in this example. The 6 tells us the rightmost X can't be a 6 so it must be a 7. That allows us to put the 6 between the 5 and 8. |
A 'Compartment' of 5,6,7 and 8 |
I have isolated this strategy from Compartment Check as it is worth looking for in it's own right. The Stranded Digit is easily understood - take the example on the right. Looking at the second row starting with the black clue 5 it cuts through a set of possible numbers for the two-cell on that row. Because the 5 is not possible (the clue) The 4's have become isolated from the 6,7,8 and 9s. That means we can discard 4 as a candidate. Similarly in the third row the 8 has isolated the 9 from the green cell. It leaves only the 7 and that is the solution. Another way to look at it is this. Write out all the remaining numbers available in a compartment. If there is a gap - then only the numbers before or the numbers after the gap can be the solution to all the cells. Does this help you remove some candidates? |
Stranded Digits |
Lets take this small section and see how it plays out: The 7 forces the 6 to the right. Above the 7 the 9 is too far away from 7 to be used - so 8 must fit there. 6 is disallowed because of the black cell clue above. And finally we can insert 7 into the last cell (marked in green). |
New Mid Section - Edit This |
This is a very easy and obvious one. The 9 in row A gives us a minimum and maximum range for that compartment of 7 to 9, ie a straight of {7,8,9}. All these numbers can be removed from the other compartment, which the solver highlights in yellow. In fact in this example, the eliminations are identical to Naked Pairs. The only remaining numbers in A3 and A4 are {7/8} which forces 7 and 8 to those cells, so any other 7s or 8s can be removed in the row. |
High/Low example 1 |
A couple of more subtle examples: Looking at the column 2 first, we have a 4-cell straight with a known 7 in it. Now the widest possible range of numbers starts from {4,5,6,7} and goes to {6,7,8,9}. Its not even necessary to have the remaining candidates viewed to see the usefulness of this. The overlap of these two sets is {6/7}. We can predict that whatever the straight, 6 and 7 will be part of it. 7 is know so we can remove the 6 from the other compartment. In a similar manner, the 3 in column 3 gives as ranges from {1,2,3} to {3,4,5}. But! 1 is already a black cell clue, so the minimum range is actually {2,3,4}. The overlap is therefore {3,4}, so 4 can be removed from C3. There is a great deal of overlap between high/low and Stranded Digit and I'm not sure what to present first. The problem is that many fewer examples of 'high/low' will be found by the solver because Compartment Check and Stranded Digit are checked first, but if you are aware of the strategy it will be very useful. It also seems to get results more at the beginning of the puzzle than the end, as the min-max ranges are greater. |
High/Low example 2 |
In the example we have three Naked Pairs - all aligned on different rows. The top row is the Pair 2/3. This attacks the cells at the start of the row (highlighted in red). Likewise the 7/8 on the second row effects the far righthand cell. And finally the 2/4 on the third row gives us a solution - marked in green. |
Setti's Rule There is now a page devoted to this strategy here. |
There are bound to be further strategies and I don't pretend to have exhausted them all on this one page. Some will be borrowed from Sudoku - I can think of Hidden Pairs and Triples, for example, and some will be unique to Str8ts. If you find a new strategy and want to share it with others we'd be delighted to explain it here and credit you with the discovery. Happy solving! Andrew Stuart |
Article created on 22-November-2008. This page was last modified on 4-February-2014, at 05:54. All puzzles on this site are trademarked and copyrighted and cannot be reproduced without permission. Copyright Syndicated Puzzles Inc, 2014, LBH |