You are given 9 square pieces (A - I), each one having in each side a number from 1 to 4, positive or negative, as shown:

        +------------+   +------------+   +------------+
        |     +1     |   |     +2     |   |     +1     |
        |            |   |            |   |            |
        |-3   (A)  +4|   |+3   (B)  -1|   |+3   (C)  -2|
        |            |   |            |   |            |
        |     -2     |   |     -4     |   |     -4     |
        +------------+   +------------+   +------------+
        +------------+   +------------+   +------------+
        |     -1     |   |     -2     |   |     +2     |
        |            |   |            |   |            |
        |+2   (D)  -4|   |-4   (E)  +1|   |+1   (F)  -3|
        |            |   |            |   |            |
        |     +1     |   |     +3     |   |     -4     |
        +------------+   +------------+   +------------+
        +------------+   +------------+   +------------+
        |     +3     |   |     -3     |   |     +3     |
        |            |   |            |   |            |
        |-2   (G)  +4|   |+2   (H)  -4|   |-2   (I)  +4|
        |            |   |            |   |            |
        |     -1     |   |     +1     |   |     -3     |
        +------------+   +------------+   +------------+

Your task is to juxtapose them forming a 3x3 grid so that "touching numbers" of each pair of touching pieces (horizontally or vertically) adds to zero.

Note: You are free to rotate the pieces.

I thought about adding up all the numbers and trying to analyze to narrow down possibilities, but I didn't do it.
Instead, I printed the page, cut out the little squares of paper, and rearranged them by hand.  Here is my solution (the numbers represent the number of degrees of clockwise rotation of the piece).  I have no idea if this is unique.

H(90)   C(0)     F(270)
G(270) A(270)  B(270)
D(90)   E(180)  I(180)

Posted by Larry on 2005-12-11 12:08:23