Help on solving daily sudoku puzzles

This recent moderate daily puzzle has got me stumped. It has three completely blank regions, including the key central one.How do I set about solving it?

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I just think you need to start with the partially complete regions and once these are solved home in on the blank regions.

So, I first look at mainly complete groups. Column a is key. If you look you'll find 1 must go in Ia amd 4 can only go in Ha. In region Aa the square Ca can only take one value 5. Assigning 5 here means that 6 must go in Ga. So that's got off to a good start a blank region noe has three squares filled in.

Now look at row C as that has five squares filled in. The missing numbers are 2,7,8 and 9. Now 2 can only go in Cg because the fortunate allocation of 2s in Gf Fh and Hi. Also you can see that the square Ci has only one possible value 7. This leaves 8;9 to assign on this row but 9 cant go in Cf so 8 must go there and 9 in Ch. Once again three squares in a previously blank region have fone and it looks a lot better to solve now.

One obvious square now is Gi which must be 5.

Attached is the puzzle with these squares solved.

Does that get you started ?

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The next easy step I found on this one was to look for the Sudoku stripe.

Looking through all the rows and columns the only place it could be is in row I at the bottom.

Once you've found that you can complete the block Gg bottom right and you are away - look at column b and row H next.

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I downloaded the puzzle into Sudoku Dragon and instead of taking the time to map all of the possibilities myself, I hit F8 on each of the blank cells. You'll find at least one cell from the start that has only one possibility. From that point, start eliminating that number from the row, region and column, and you'll find others. It kind of opens up from that point. There are a couple of naked pairs that appear just from eliminating possibilities. Try that first, and if you still can't solve it, I'll be glad to send you my results.

Thanks, Ray

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Trying to take my problem solving skills to the next level and it does not appear that X-Wing or Swordfish methods apply -- but since I'm new to those methods, I may have missed something. - This puzzle has me stumped, what should I do next ?

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It does turn out to be quite a difficult puzzle but I do not think you need to use X-Wing/Swordfish to solve it.

You are correct in that there are no straightforward squares to solve. However, the hidden/naked twin and shared subgroup strategies do remove of the posibilities and then allow squares to be solved.

Take a look at the last column (column i) there are six unallocated squares with possibilities Ci (57) Di (18) Ei (148) Fi (89) Gi (4579) Hi (5789). This does not look all that promising but there is a pattern here.

Ignore extra possibilities four of these squares form a chain of four possibilities with numbers 5;7;8;9 in Ci (57) Hi (78) Fi (89) and Gi (95) to take it back to 5. Because of this the numbers 5;7;8;9 can not occur elsewhere in row i so both the 8 in Di and the 8 in Ei are not actually possible. This further allows 1 to be safely allocated to Di and 4 to Ei.

This should hopefully unlock the puzzle for you.

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