de Bruijn sequence

k is the language (0..k-1). n is the length of the string.
The de Bruijn sequence is the shortest way one can combine all the $k^n$ possible combinations (strings)
if one is allowed to overlap the different combinations.
The total length of the sequence is $k^n+n-1$ (the $+n-1$ part is for the "around the corner" cases).

• Wikipedia: De_Bruijn_sequence
• My plain JavaScript version with some more comments: debrujn.js
• My old CGI/Perl version: debruijn.cgi