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Conference dypss1::brain_bogglers

Title:Brain Bogglers
Notice:BRAIN_BOGGLERS is, like, back in business, totally
Moderator:BUSY::SLAB
Created:Mon Jul 13 1987
Last Modified:Mon Jun 02 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:1441
Total number of notes:13981

1431.0. "Cross sums" by BUSY::SLAB (As you wish) Mon Jan 27 1997 13:45

    
    	I got several puzzle books recently, and 1 of them had 4 of
    	these puzzles in it.

    	They're set up like crossword puzzles, but instead of words
    	for clues and answers you use numbers.

    	Example:

    

	                  -------------------
                          | 21\ | 18\ | 24\ |
	            -------------------------
                    |16\16|     |     |     |
    	      -------------------------------
    	      |15\30|     |     |     |     |
    	-------------------------------------
    	| \35 |     |     |     |     |     |
    	-------------------------------------
        | \4  |     |     |
    	-------------------
    	      |     | 17\ |
    	-------------------
    	| \13 |     |     |
    	-------------------
    	| \11 |     |     |
    	-------------------

    	Use the digits 1-9 only and fill in the puzzle such that all
    	indicated sums are attained.  And any digit can not appear
    	more than once in the same answer.

	The number preceding the slash [\] indicates the sum of numbers
	in blocks below, and the number following the slash [\] indicates
	the sum of numbers in blocks to the right.

	If this puzzle isn't solvable, tell me why.  I just whipped it up,
	and I know that it can be solved, but I can't guarantee that this
	can be reasoned out such that the answers are guaranteed unique.
    
T.RTitleUserPersonal
Name
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1431.1Partial solutionCHEFS::STRANGEWAYSAndy Strangeways@REO DTN 830-3216Tue Jan 28 1997 05:1944
    Interesting puzzle.
    
    Partial solution follows form feed.
    
    The bottom left part has a unique solution:
    
      5
      1 3
      2
      4 9
      3 8
    
    To work this out, note that 17 can only be {8,9}. The only
    possibilities for 11 are therefore {8,3} and {9,2} and the only
    possibilities for 13 are {8,5} and {9,4}.
    
    Combining all these, we have 
    
      ?		or	?	or	?
      1 3		1 3		3 1
      ?			?		?
      4 9		5 8		5 8
      3 8		2 9		2 9
    
    in the bottom left.
    
    Observe that 35 must be {5,6,7,8,9}. This is not compatible with the
    last two possibilities above and only fits with the first in one way:
    
      5 
      1 3
      2
      4 9
      3 8
    
    As to the top right, there are at least two solutions:
    
        5 4 7				  5 4 7
      6 7 8 9				7 9 6 8
      7 9 6 8		and		6 7 8 9
    
    I haven't done an exhaustive search, though.
    
    Andy.
1431.2BUSY::SLABAs you wishTue Jan 28 1997 11:386
    
    	Yup, your logic is correct.
    
    	Now picture a 15x15 grid that's 4x as hard and you see what I
    	went through this w'end.  4 of them.  8^)
    
1431.3DYPSS1::s_coghill.dyo.dec.com::CoghillSSteve Coghill, NSIS Solution ArchitectTue Jan 28 1997 14:1782
I love these puzzles.  I think PennyPress's puzzles are
more challenging than Dell's puzzles.  

I just worked a couple that had a new (for me at least) twist
on them.  Each group had to had at least one zero in the
answer.  Had to throw all my tricks out of the window for this one.

Some helps:

You can use the following to narrow down answers.  Look for intersections 
of the following combinations.  It can give the answers, a subset of 
possible digits, or a subset of excluded digits.  Examples:


In these examples there is only one solution each

	+---+---+---+
	|***|***|x/4|
	+---+---+---+
	|***|***| 3 |
	+---+---+---+
	|x/3| 2 | 1 |
        +---+---+---+

	+---+---+---+
	|***|***|/17|
	+---+---+---+
	|***|***| 8 |
	+---+---+---+
	|/16| 7 | 9 |
        +---+---+---+

In this example you know where to put the 5

	        +---+
		|/29|
		+---+
		| ? |
		+---+
		| ? |
		+---+
		| ? |
+---+---+---+---+---+
|/11| ? | ? | ? | 5 |
+---+---+---+---+---+

		
Two Digit Answers:

3 = 1 + 2
4 = 1 + 3
16 = 7 + 9
17 = 8 + 9

Three Digit Answers:

6 = 1 + 2 + 3
7 = 1 + 2 + 4
23 = 6 + 8 + 9
24 = 7 + 8 + 9

Four Digit Answers:

10 = 1 + 2 + 3 + 4
11 = 1 + 2 + 3 + 5
29 = 5 + 7 + 8 + 9
30 = 6 + 7 + 8 + 9

Five Digit Answers:

15 = 1 + 2 + 3 + 4 + 5
16 = 1 + 2 + 3 + 4 + 6
34 = 4 + 6 + 7 + 8 + 9
35 = 5 + 6 + 7 + 8 + 9

Six Digit Answers:

21 = 1 + 2 + 3 + 4 + 5 + 6
22 = 1 + 2 + 3 + 4 + 5 + 7
38 = 3 + 5 + 6 + 7 + 8 + 9
39 = 4 + 5 + 6 + 7 + 8 + 9

1431.4BUSY::SLABAs you wishTue Jan 28 1997 14:515
    
    	I love 'em, too, but had never seen them before Saturday.
    
    	Now I'll have to see if I can find an entire book full of them.
    
1431.5RHETT::MOORETue Jan 28 1997 15:025
    you can usually find books of them at newstands.  
    
    What's interesting is how much the degree of difficulty varies.  Some
    are almost trivially easy, while others are real brainstormers.
    
1431.6DYPSS1::s_coghill.dyo.dec.com::CoghillSSteve Coghill, NSIS Solution ArchitectTue Jan 28 1997 16:193
Dell publishes a couple of Math only puzzle mags every year.  Dell's 
and PennyPress's monthly mags have between 4 and 10 of the puzzles in 
each edition.
1431.7BUSY::SLABAs you wishWed Jan 29 1997 13:3810
    
    	I have an "Official" [I think that's the actual name of it] puzzle
    	book with a couple of these in it also, but they call them "Cross
    	additions".
    
    	But these are rather inconvenient since they're set up in true
    	crossword puzzle form with a list of across/down clues, and it's a
    	pain to go back and forth between clues/grid when you're trying to
    	think an answer through.
    
1431.8BUSY::SLABBeware of geeks baring griftsThu Feb 06 1997 12:419
    
    	I picked up the April PennyPress and they did have 2 of these in
    	it.  However, I don't like the fact that they give you a "starter"
    	answer ... it really isn't necessary.  Well, not for me, anyways.
    
    	Both puzzles were very easy at 1st ... or maybe I'm getting good
    	at them or something.  But the middle sections of both weren't
    	very easy at all.
    
1431.9DYPSS1::s_coghill.dyo.dec.com::CoghillSSteve Coghill, NSIS Solution ArchitectFri Feb 07 1997 10:444
Depending on what issue you get PennyPress has some puzzles with no starters.

I looked throu mine and it seems that the first two puzzles have the starters 
and the rest don't.  If the issue has only two puzzles then you get a starter.