This month's problem comes from my favorite math site: mathpuzzle.com. A snake is a sequence of unit line segments that are non-overlapping except that each one begins where the previous one ends. A d degree snake is a snake all of whose angles with the horizontal are multiples of d. We are interested in the longest d degree snake that will fit inside a square of side s.
The discussion at mathpuzzle.com has mostly been about the longest snakes that can fit inside a square of side 2:
s=2, d=45 length 15 Found by Roger Phillips
s=2, d=30 length 20 Found by Susan Hoover
s=2, d=22.5 length 32 Found by Jon K McLean
What are the longest 30o snakes you can find in some small squares? How about 22.5o snakes? What about the longest snakes that fit inside rectangles? circles?
ANSWERS
Here are the longest known 45o snakes inside small squares:
s=1/√2, d=45 length 1
s=1, d=45 length 4
s=2-1/√2, d=45 length 7
s=1+1/√2, d=45 length 10
s=2, d=45 length 15 Found by Roger Phillips
s=3-1/√2, d=45 length 17
s=1+√2, d=45 length 19
s=4-√2, d=45 length 21
Here are the longest known 30o snakes inside small squares:
s=√3/2, d=30 length 2
s=1, d=30 length 4
s=3-√3, d=30 length 7
s=3/2, d=30 length 10
s=(5-√3)/2, d=30 length 11
s=7/2-√3, d=30 length 13
s=1+√3/2, d=30 length 14
s=(9-3√3)/2, d=30 length 15
Here are the longest known 22.5o snakes inside small squares:
s=.708, d=22.5 length 1
s=.924, d=22.5 length 2
s=1, d=22.5 length 6
s=1.077, d=22.5 length 7
s=1.229, d=22.5 length 9
s=1.323, d=22.5 length 10
s=1.542, d=22.5 length 12
s=1.690, d=22.5 length 16
s=1.914, d=22.5 length 18
Here are the longest known 18o snakes inside small squares:
s=.810, d=18 length 2
s=.952, d=18 length 3
s=1, d=18 length 6
s=1.049, d=18 length 9
s=1.147, d=18 length 11
s=1.289, d=18 length 12
s=1.310, d=18 length 13
Here are the longest known 45o snake loops inside small squares:
s=1, d=45 length 4
s=1+1/√2, d=45 length 8
s=2, d=45 length 12
s=3-1/√2, d=45 length 16
s=4-√2, d=45 length 18
Here are the longest known 30o snake loops inside small squares:
s=1, d=30 length 5
s=3/2, d=30 length 8
s=5/2-√3/2, d=30 length 12
Here are the longest 45o snakes inside some small rectangles:
0
1/√2
1
2-1/√2
1+1/√2
2√2-1
1/√2
1
2-1/√2
1+1/√2
2
Here is the longest 30o snake inside a 2x3 rectangle:
Trevor Green and
Jeremy Galvagni worked on an efficient snake in rectangles of width 1 and d small. The basic idea is shown below:
Serhiy Grabarchuk found the longest 30o snakes inside regular polygons:
d=30 length 6
d=30 length 11
d=30 length 14
d=30 length 18
Serhiy Grabarchuk also found the longest 30o snake on the surface of a unit cube. The red lines are on the front faces, and the blue lines are on the back faces.
In November 2006, Al Zimmerman held a contest to find the largest possible 360/N degree snakes inside a circle of diameter D, for small N and D. Below is a table showing the best results.