So when do I need the good memory? Thats only when I cant find anything else and start trailing. If you systematically go through all rows like this you will find all naked singles in no time. This trick is also efficient when looking for hidden singles in rows or columns (try it on row 6). R4c2 has 6, 7 and 8 in the same column, so theres a naked single (2). These are the 4 numbers that go in the four empty cells, so now I compare each cell against these numbers. If I wanted to find naked singles in this puzzle, I would start with row 4 that already has 5 numbers, then count: . I start with the rows/columns that have most numbers already, then I count from 1 to 9, leaving out all the numbers already in the row. I rather look for them one row or column at a time. Going through the whole puzzle cell by cell is very timeconsuming. The hidden singles are usually easy to spot, just picture horisontal and vertical lines going through all instances of a particular number and find the only empty square. I guess most of you use pencilmarks to spot singles, so the most important thing to improve if you want to solve without pencilmarks is not your memory, but your ability to spot singles. Apart from this I memorize locations of pairs and triplets, but the rest of the information about each cell I put aside as soon that I can see that it doesnt help me at the moment. Only when I make a reduction through some other technique, like x-wing, uniqueness etc., I memorize the reduced candidates. As most of the impossibles can be read from the column, row and box of each cell, there isnt really that much to remember. Instead of memorizing possible candidates, I memorize impossible candidates. So what Im interrested in is these reduced possibilities. Most puzzles can be solved exclusively with naked or hidden singles, then what's the point in knowing that a cell can hold numbers 1,2,6 and 7? In fact, all numbers are solved by naked or hidden singles, all other techniques only reduce possibilities.

When I finally realised that this is pointless, my solving improved significantly. When I started doing Sudoku I often found myself trying to memorize possible values for cells, drawing a mental pencilmarkgrid.

There is simply so much information to be found in any grid, that one can't remember it all. The most important thing I've learned so far is to choose what information to memorize. My answer is yes, but I hardly ever use it. If anybody else has got any good tips on solving without pencilmarks, please post them here and we can try to make a little collection of these techniques.įirst of all, whenever I say that I solve without pencilmarks, peoples first reaction is: 'then you must have a really good memory'. First I'll give you some tips that I've found usefull, then I'll take you through a step by step solution of a couple of extreme puzzles, the way I solve them, and hope that you can follow without making any own pencilmarks. Now I wish to show you that none of those are true. I often read comments like 'no other than the easiest puzzles can be solved without pencilmarks' or 'techniques that are impossible for human solvers.'. The more I read posts on this forum, the more I get the feeling that I'm the only person in the world who solve exclusively without pencilmarks, regardless off difficulty.

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