30 May
2022
30 May
'22
2:43 p.m.
On May 30, 2022, at 1:16 AM, Ralph Corderoy
<ralph(a)inputplus.co.uk> wrote:
Hi Bakul,
For permutations I just use this k program:
$ cat perm.k
p:{:[1<x;,/(>:'(x,x)#1,x#0)[;0,'1+_f x-1];,!x]}
perm:{x@p[#x]}
$ k perm.k
perm "abc"
("abc"
"acb"
"bac"
"bca"
"cab"
"cba")
I won’t bother explaining but p n returns all permutations of
indices 0..n-1. Then perm is easy to construct. Similarly easy to
insert | between strings but your solution is much more in the spirit
of regexp and faster than my brute force solution!
Also, thanks for catching the anchoring error!
You can write a program to generate all
permutations and use that as
your regexp. For example abc maps to abc|acb|bac|bca|cab|cba.
Being lazy, I tend to use a shell's brace expansion and then whittle it
down to generate permutations. I keep thinking it's surprising there's
no Bell Labs program to produce them given there's things like
factor(1).
The brace expansion is wasteful as it's going from n**l down to n! and
it can result in the old bash here not responding to SIGINT for a while
if it's producing gazillions.
$ printf '%s\n' {b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y}\
{b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y} |
egrep -v '(.).*\1' |
fgrep -x -f - /usr/share/dict/words
ladybug
$
--
Cheers, Ralph.