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## Re: TPR1 post-mortem

From:
Marcelo E. Magallon
Date:
March 8, 2002 06:22
Subject:
Re: TPR1 post-mortem
Message ID:
20020308141610.GA30975@informatik.uni-stuttgart.de
```>> Jason Purdy <jason@journalistic.com> writes:

> Is that #*1.11%10 a number theory to get to the same number?  How did
> someone recognize that pattern? (my advanced calculus/comb math being
> a lil' rusty)

I don't know others, but I started by looking at the input and output,
like this:

0   0
1   1
... ...
9   9
10   1
11   2
12   3
... ...
18   9
19   1
20   2

As you can see it's just a series of 1 .. 9, except for 0.  With that
in mind my first I tried something like (0,(1..9)x11)[\$n].  Actually,
before that I tried something more like (0,(1..9)x2)[\$a+\$b] (where \$a
and \$b are the digits).  Then I noticed that I could get the same
result using %9 and some conditionals.  After putting this stuff aside
and having some sleep I just pictured the thing as a table like this:

0   1   2   3   4 ...
0   00  11  22  33  44 ...
1   10  21  32  43  54 ...
...
8   80  91  12  23  34 ...
9   90  11  22  33  44 ...

which made it kind of evident that 111%100 should do what I wanted.
*Then* I had a different problem to solve :-)

> What is \G ... \$&?  Gotta dig out my Camel book again.

Check out perlre and perlvar and the "g" option to m//.

A question of my own: why doesn't

s/\B.\B/\$&\$&/g

work as I expect, namely abcd -> abbccd.  I really can't figure it out
by reading the docs.

TIA,

Marcelo

```