From: Ralph Corderoy <ralph@inputplus.co.uk>
To: Computer Old Farts Followers <coff@tuhs.org>
Subject: [COFF] Re: Grep has gone overboard
Date: Mon, 30 May 2022 10:19:35 +0100 [thread overview]
Message-ID: <20220530091935.073CA21F37@orac.inputplus.co.uk> (raw)
In-Reply-To: <DB37381E-6260-4974-B1B7-C28E0241D5F1@iitbombay.org>
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]}
I was thinking it looks like APL and it turns out to be a descendant.
https://en.wikipedia.org/wiki/K_(programming_language)
That pushed me into writing an awk-permutation generator. It's
inefficient as it keeps altering $0 which cascades into re-working $1,
etc., even if that's lazily done. Still, it sufficies for the small
cases I typically need.
$ cat perm
#! /bin/awk -f
function perm(s, f, l, t) {
if (!NF) {
print substr(s, 2)
return
}
l = $0
for (f = 1; f <= NF; f++) {
t = $f
$f = ""; $0 = $0
perm(s " " t)
$0 = l
}
}
{ perm("") }
$
$ ./perm <<<''
$ ./perm <<<1
1
$ ./perm <<<'1 2'
1 2
2 1
$ ./perm <<<'1 2 3'
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1
$
$ time ./perm <<<'1 2 3 4 5 6 7 8 9' | wc -l
362880
real 0m5.421s
user 0m5.406s
sys 0m0.082s
$
$ dc <<<'9 8*7*6*5*4*3*2*p'
362880
$
--
Cheers, Ralph.
next prev parent reply other threads:[~2022-05-30 9:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-30 4:12 [COFF] " Dave Horsfall
2022-05-30 4:47 ` [COFF] " Bakul Shah
2022-05-30 6:35 ` Michael Kjörling
2022-05-30 6:51 ` Bakul Shah
2022-05-30 8:26 ` Ralph Corderoy
2022-05-30 8:01 ` Ralph Corderoy
2022-05-30 8:16 ` Ralph Corderoy
2022-05-30 8:43 ` Bakul Shah
2022-05-30 9:19 ` Ralph Corderoy [this message]
2022-05-30 7:38 ` Ralph Corderoy
2022-05-30 7:44 ` Ralph Corderoy
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