## Swamped by candidates

Advanced methods and approaches for solving Sudoku puzzles

### Swamped by candidates

I was looking at some Pocket PC sudoku software and I found one that would be perfect except that it only allows up to four candidates to be entered in each cell. When I solve a sudoku on paper I tend to have on average four to six candidates per cell to start with (the ones with 1-3 candidates are precious!). I find them impossible to solve without putting in the candidates first (after entering the obvious slice & dice numbers). For me this applies from level medium upwards.

Can you solve hard puzzles without candidates? Any tips for avoiding getting swamped by the number of candidates?
apatt

Posts: 26
Joined: 28 July 2005

### Re: Swamped by candidates

apatt wrote:Can you solve hard puzzles without candidates? Any tips for avoiding getting swamped by the number of candidates?

Try testing for one number at a time. Don't start with writing down all candidates for a box.
Write down all candidates for a certain number.
If the number is too hard. Wait with it until later.

Also. Make sure that you master the basic solving techniques. Missing some implications may increase the number of candidates that you write down.

http://www.simes.clara.co.uk/programs/sudokutechniques.htm
(techniques up to and including Hidden Subset.)

I hope that helps.

/Martin
[/quote]
govert

Posts: 3
Joined: 19 August 2005

### Swamped by candidates - also

This week was a first, M-F puzzles were solved in reasonable time - using logic and elimination. The Saturday puzzle was another story, ended up with fewer empty boxes than last Satuday - but still had a minimum of two candidates per remaining squares. If the puzzle instructions suggest that guessing is allowed - but not recommended - how can the remaining candidates be slimmed down without a trila and error (aka guessing)? Be gentle - I'm still a novice!
GFox49

Posts: 3
Joined: 13 August 2005

There are various techniques, given exotic names like xwings, ywings, swordfish, forcing chains, colouring, xy chains. Which of them could help you is hard to say without seeing both the original grid, and where you're up to.

For help on some of the above techniques, take a look here

Simes
simes

Posts: 324
Joined: 11 March 2005
Location: UK

### Re: Swamped by candidates - also

GFox49 wrote:This week was a first, M-F puzzles were solved in reasonable time - using logic and elimination. The Saturday puzzle was another story, ended up with fewer empty boxes than last Satuday - but still had a minimum of two candidates per remaining squares. If the puzzle instructions suggest that guessing is allowed - but not recommended - how can the remaining candidates be slimmed down without a trila and error (aka guessing)? Be gentle - I'm still a novice!

Sounds like you're playing in the Chicago Sun-Times, like me. Today's puzzle (Saturday August 20) is probably the hardest I've encountered yet. I first encountered the game only 2 or 3 weeks ago when the paper started to print them, and I've done most of them without much trouble.

But today's, man... I'm stuck right now and gonna go to bed before I go nuts. I'll try again later -- maybe just start fresh. I am stuck with so many squares that are either one number or another -- only 2 choices! But I can't seem to narrow any down...
walkure

Posts: 3
Joined: 20 August 2005

Walkure and (maybe) Gfox. I, too, have been working the Sun-Times puzzles and only first encountered Sudoku when they began printing them. I've been 11 for 11 so far, but last Saturday's tripped me up for a while and I had to start over once. All in all, it took me a good 3 hours to solve. Kinda wish they had them on Sundays, too!

I'm about 5 minutes from starting yesterday's puzzle.
The Central Scrutinizer

Posts: 22
Joined: 10 August 2005

### Sun-Times

Central Scrutinizer -- good luck with the Saturday 8/20/05 puzzle!!! I will look at it again later tonight probably. I may just start over, since I was only able to get about 12 numbers, and am left with so many squares with 2 candidates! Perhaps I made a mistake that is throwing me off...

The "very easy" puzzles on Monday and Tuesday will seem boring after this one!
walkure

Posts: 3
Joined: 20 August 2005

walkure, I finished that Saturday puzzle up on the way to work this morning. I also was to a point where I had about 11 numbers placed and too many candidates, but I kept scanning and noticed there were a few eliminations that I had missed. That made all the difference.

The 59 pair in row 3 of box 2 that forced the 27 pair in box 3, which in turn forced a single 9 in row 2 was interesting.

Be on the lookout for pair combinations in boxes that can eliminate those candidates in the affected column or row.
The Central Scrutinizer

Posts: 22
Joined: 10 August 2005

Look for numbers that cannot be in a cell, it's a great way of removing candidates.

Cheers.
King Voodoo

Posts: 7
Joined: 05 July 2005

Can someone please post the puzzle from the Aug 20th edition of the Chicago Sun Times? After reading about it here, I would love to try it.

Plus it was my birthday that day, so why not try to solve it.

Thanks,
nj3h
nj3h

Posts: 47
Joined: 07 July 2005

nj3h, unfortunately the Sun-Times website only posts the puzzles from the last 6 days, so I can’t get it from their site.

I may have it at home, though. I’ll look after work tonight.
The Central Scrutinizer

Posts: 22
Joined: 10 August 2005

### Candidates, schmandidates!

Since my last (and until now - only) post I hunkered down and re-thought the logical method I thought would work. For me, I find it best to first work each of the 3x3 boxes, checking both row and column for any possible candidates. I write each candidate in very small print inside each separate box. This allows me to find the single candidates - crossing out the same numbers in the row/column and 3x3. Then I continue reducing by working rows and columns - getting down to the multiple candidates squares. From there, it's relatively simple to work through the puzzle using the squares that have the same two candidates in a row or column. Process of elimination/attrition is all I need from there to finish. After that one Saturday (8/20) stumper, I retooled my solving technique and as of today am 12 for 12 the past two weeks. Genius? - No, Sudoku savant? - most definitely! Time for Judge Wapner, Judge Wapner....
GFox49

Posts: 3
Joined: 13 August 2005