Code Golf: Ulam Spiral
code-golf, language-agnostic, rosetta-stone
Solution
Golfscript - 92 Characters
~.(:S+,:R{S\-:|;R{S-:$|>' *'1/[|$.|]2/@:d|~)$<!^=~:$;:y.*4*$-y-)2d*$y-*+:$,{)$\%!},,2==}%n}%
97 characters ~.(:S+,:R{S\-:|;R{S-:$|>' *'1/[|$.|]2/@:d|~)$<!^=~:$;:y.*4*$-y-)2d*$y-*+.1=3*+:$,2>{$\%!},!=}%n}%
99 characters ~.(:S+,{S-}%:R{~):|;R{:$|>' *'1/[|$.|]2/@:d|~)$<!^=~:$;:y.*4*$-y-)2d*$y-*+.1=3*+:$,2>{$\%!},!=}%n}%
100 characters ~:S.(+,{S(-}%:R{~):|;R{:$|>' *'1/[|$.|]2/@:d|~)$<!^=~:$;:y.*4*$-y-)2d*$y-*+.1=3*+:$,2>{$\%!},!=}%n}%
101 characters ~:S.(+,{S(-}%:R{~):v;R{:$v>:d;' *'1/[v$.v]2/v~)$<!d^=~:$;:y.*4*$-y-)2d*$y-*+.1=3*+:$,2>{$\%!},!=}%n}%
Problem
The Challenge The shortest code by character count to output Ulam's spiral with a spiral size given by user input. Ulam's spiral is one method to map prime numbers. The spiral starts from the number 1 being in the center (1 is not a prime) and generating a spiral around it, marking all prime numbers as the character '`*`'. A non prime will be printed as a space '` `'. alt text http://liranuna.com/junk/ulam.gif Test cases ``` Input: 2 Output: * * * * Input: 3 Output: * * * * * ** * * Input: 5 Output: * * * * * * * * * * * ** * * * * * * * * * ``` Code count includes input/output (i.e full program).