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 26th June 2020 Extra - 15x15 
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Posted on: Sun Jun 27, 2021 11:33 am

Posts: 814
Location: Dublin, Ireland
Joined: Tue Mar 01, 2016 10:03 pm
Post 26th June 2020 Extra - 15x15
I usually find that I do the 15x15 in a number of chunks, saving it at various points and coming back to it later. I often run into blind alleys and have to retrace my steps. This often involves going back to the last time I saved it, but sometimes I have to start all over again.

As a result, I have no idea how long in total I spend doing each of these puzzles, as the time shown at the end does not include time spent going down blind alleys and then going back to earlier saved versions.

So I decided to see if I could do yesterday’s puzzle in one go. This meant being very careful and methodical about each step and not doing any “trial and error” runs. I managed to actually complete it in one go, but it took me quite a while - seconds to be precise.

I’d be interested to hear how other people approach these extra large puzzles and how long it usually takes you to solve them.


Posted on: Sun Jun 27, 2021 4:42 pm

Posts: 590
Joined: Wed Apr 16, 2014 9:20 pm
Post Re: 26th June 2020 Extra - 15x15
I try to solve them in one go.

I rarely ever fill in all the possibilities for all the cells. If I have to do that I am not seeing something. It is a sign that the puzzle was difficult for me.

I avoid large cages until I can eliminate possibilities from having solved other cages in various rows or columns.

I try to avoid using T & E in the puzzle itself; I try to work out possibilities in my head. By the time, I am doing this in my head, I have tried to reduce the number of possibilities to two or three choices. I often repeat my logic two or three times to be sure I am not making a mistake.

For me, doing it in different solving sessions means I would lose my train(s) of thought and I would rather stay focused, concentrated on the puzzle until it is done.


Posted on: Tue Jun 29, 2021 9:50 am

Posts: 148
Joined: Sun Jan 31, 2016 7:52 am
Post Re: 26th June 2020 Extra - 15x15
paulv66 wrote:
I’d be interested to hear how other people approach these extra large puzzles and how long it usually takes you to solve them.

My advice for the 15x15 puzzles would be:

1. Avoid too many pencil marks, try to only use pencil marks when there are only 2 or 3 possible values for a cell. It can quickly become a confusing mess of pencil marks in the larger puzzles

2. Ignore any large cages for as long as possible.

3. Don't forget the basics, every row and column has each number only once. In a large puzzle it seems too hard to look for every value in every row and column, but if you look for areas with several limiting factors such as multiplication cages and solved cells you will be surprised how many cells can be solved. In the 15x15 from 26th June there are probably more cells solved using this method than anything else.

4. Trial and error is probably less useful on the larger puzzles.

5. The large puzzles are rated as difficult, and I would agree that they are difficult because they are large and they take a lot of work to complete, but don't let yourself get bogged down looking for complex methods to make some progress. Do what is easiest first. On this puzzle I did not do anything more complicated than finding paired values that are in a 2 cell cage.

I am fairly slow at solving the larger puzzles, I don't take note of how long it takes. I like to make the puzzles as large as possible on the screen and that becomes less successful as the puzzles increase in size.

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