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Cubic Diagonals and Edges (Posted on 2009-04-30) Difficulty: 3 of 5
This is the net map of the outer surfaces of the 20 edge cubes that represents
a 3 x 3 x 3 'parent' cube (like in a Rubik cube).

A B C
D E
F G H
A D F
I J
M N O
F G H
J K
O P Q
H E C
K L
Q R S
C B A
L I
S T M
O P Q
N R
M T S

Assign unique values from 1 to 20 to the letters A-T such that the sum of each pair of diametrically opposite cubes is to be the same as all others while the sum of each set of edge cubes may not differ from that of any other set by more than one.

Eg, diagonals:
                    A + Q = N + E = C + O ...(etc)
and edge cubes:     A + B + C = C + E + H = F + G + H ...etc,
                or (A + B + C) ±1 = C + E + H
                                  = F + G + H ....(etc) 
Note: The problem's development and my solution used a spreadsheet; as such a well-constructed sheet could enable a solution. Although this problem may lend itself to a programmed solution I would appreciate seeing attempts of a more manual basis within the first 24-48 hrs.

  Submitted by brianjn    
No Rating
Solution: (Hide)
It should be apparent that the diagonal sums are 21, 1+20, 2+19 ....

Assigning unique values to the letters of the map and summing the 12 edges yields an average of 31.5. Since the edges sums are to be no more than one different from any other we require edges of 31 and 32. This occurs six (6) times with 31 and 32 being diagonally opposite.

My value table was:
 A  B C  D  E F  G H I J  K  L  M N  O P  Q R  S T
10 19 3 16 20 6 17 8 9 7 12 14 13 1 18 2 11 5 15 4

My edge sums, and subsequent pairings were formed from:
ABC  32    OPQ  31
ADF  32    QRS  31
CEH  31    MNO  32
FGH  31    MTS  32
FJO  31    CLS  32
AIM  32    HKQ  31 
10 19 3
16   20
6 17 8
10 16 6
9   7
13 1 18
6 17 8
7   12
18 2 11
8 20 3
12   14
11 5 15
3 19 10
14   9
15 4 13
18 2 11
1   5
13 4 15

Realising that there would be multiple solutions I thought that I had assigned a specific value to A to limit such a range. However that has not been the case. Although this is my one solution, Charlie again has given us a comprehensive range. My comments above however do give a short summary of the nature of the problem.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Puzzle AnswerK Sengupta2024-01-13 21:33:54
re(2): computer solutionsCharlie2009-05-03 12:13:31
re: computer solutionsbrianjn2009-05-03 10:31:15
re: computer solutions--the programCharlie2009-05-01 12:02:43
Solutioncomputer solutionsCharlie2009-05-01 11:59:18
Restraintbrianjn2009-05-01 10:09:41
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