Jacobs’ Sudoku for the Brave


Coming back to basics, this post reviews Charlie Jacobs’ collection of basic puzzles, Sudoku for the Brave. The book has no commentary at all.  Just puzzles and solutions.

jacobs review tableCharlie labels his 200 puzzles “Extreme”, but they don’t come close to that.  I did find them challenging enough for the commute or airlines flight.

I was able to leave the advanced techniques  bv count columns out of the review table, because none of the 10 puzzles I worked through actually got that far.  Review table conventions are on the page linked above.  Preselected were Brave 6 and every 20th thereafter.

Two collapsed (—) in box marking.  One of these, Brave 146, brought something I’d never seen, a naked septuple (7 locked numbers).

Of course, these results assume you are starting with the slink marking bypass, finding all unit slinks in line marking, then finding all remaining clues and candidates in line marking.  Otherwise, you might happen upon all kinds of fish, chains, loops, and ALS.  Here we seek to find these only when they are needed.

For highlights, below are two grids from Sudoku for the Brave.  You could recover the givens and see if your counts and line marking are better than mine. That’s quite possible.  Or better yet, get a copy of Charlie’s book and have a completely independent look.

In Brave 26, the naked triple strikes on the last row of line marking, which is tough enough to leave your pencil marked copy an unholy mess.

Brave 26ntThe triple leaves a naked pair, giving N5, which  triggers the collapse.  I wouldn’t want  to wade through the sea of number scanned candidates that Brave 26 generates.

Brave 146 septupleNext is the grid of Brave 146, just as the  septuple develops in the SE box.

No clues in the box and the candidates of 8 numbers are present by virtue of slinks. Two candidates of the ninth number, 6, are required in r89c7. 6 can be placed nowhere else in SE, therefore the 7 cells are occupied by 7 numbers.  Two clues, a naked pair, and an immediate collapse are the results.

You can own this septuple by building up to it. The bypass and box marking traces are given below, as a checkpoint.

Brave 146 trace

Next week, I  return to exocets with Unsolvable 197, to properly absorb and acknowledge David P. Bird’s application of his Junior Exocet rules to this puzzle, and to apply another form of Chute Lettering to 197. Bird’s solution of 197, and 190, in comments to the Unsolvables page convinces me that I misinterpreted his compendium conditions and rules on JE’s.

My adventures with the exocet Unsolvables is bringing welcome attention, and hopefully, some good human solving insights, from EnjoySudoku  contributors.  I regret that I am not able to join in on the forum itself, while keeping to my weekly posting schedule at the same time. Maybe later.

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About Sudent

My real name is John Welch. I'm a happily married, retired professor (computer engineering), timeshare traveling, marathon running father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. The blog is about Sudoku solving. It covers how to start, basic solving to find candidates efficiently, and advanced solving methods in an efficient order of battle. It is about human solving methods, not computer solving.
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