can't find mistake. using sort and slice in regex

rsFalse has asked for the wisdom of the Perl Monks concerning the following question:

Hi,
I tried to solve Problem 18 from Project Euler.
I'm trying to execute that substitution multiple times, but only once it worked as I expected:
s/(\d+)(?= (\d+))/ (sort {$b<=>$a}($1, $2))[0] /eg;
Do you see where do I do the mistake?

Details:

$\ = $/;
undef @max;
for (reverse <DATA>){
    chomp;
    print;
    s/(\d+)( )?/ $1 + (shift @max) . $2 /eg;
    print;
##    s/(\d+)(?= (\d+))/ $1 > $2 ? $1 : $2 /eg;  ##  works
##    s/(\d+)(?= (\d+))/ do {local $\; print "[$1|$2]"}, 
##    (sort {$b<=>$a}($1, $2))[0] /eg;  ## works
    s/(\d+)(?= (\d+))/ (sort {$b<=>$a}($1, $2))[0] /eg;  ## doesn't
    print;
    print "------------";
    @max = split
    }
    
__DATA__
75
95 64
17 47 82
18 35 87 10
20 04 82 47 65
19 01 23 75 03 34
88 02 77 73 07 63 67
99 65 04 28 06 16 70 92
41 41 26 56 83 40 80 70 33
41 48 72 33 47 32 37 16 94 29
53 71 44 65 25 43 91 52 97 51 14
70 11 33 28 77 73 17 78 39 68 17 57
91 71 52 38 17 14 91 43 58 50 27 29 48
63 66 04 68 89 53 67 30 73 16 69 87 40 31
04 62 98 27 23 09 70 98 73 93 38 53 60 04 23
[download]

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Re: can't find mistake. using sort and slice in regex by ikegami (Patriarch) on Feb 09, 2015 at 17:43 UTC
`(sort {$b<=>$a}($1, $2))[0]` [download] and `(sort {$b<=>$a}("$1", "$2"))[0]` [download] produce different result, which points to a mishandling of magic variables in `sort`.	[reply] [d/l] [select]
Re: can't find mistake. using sort and slice in regex by Laurent_R (Canon) on Feb 09, 2015 at 18:59 UTC
You're not saying how it doesn't work. Wrong result? Can you please show where it is getting wrong, then? One thing I might try to change in your code is to replace your `sort` line with this: `s/(\d+)(?= (\d+))/ $1 > $2 ? $1 : $2/eg;` [download] as using sort just for retrieving the largest of two variables seems a bit of an overkill. I think that the intent gets clearer. But this will probably produce the same result. So we are back to my first question: where is it wrong? Update: I had not seen that the line I suggested just above was in your commented out code lines. I tried the code as you have it and also with the code line suggested just above, they seem to produce the same output. Je suis Charlie.	[reply] [d/l] [select]
Re: can't find mistake. using sort and slice in regex by LanX (Saint) on Feb 10, 2015 at 01:54 UTC
I can't reproduce your or Ikegami's problem, works fine for me.š `DB<124> $a=42; $a =~ s/(.)(.)/(sort { $a <=> $b } $1,$2)[0]/e ;$a => 2 DB<125> $a=42; $a =~ s/(.)(.)/(sort { $a <=> $b } "$1","$2")[0]/e ;$ +a => 2 # UPDATE with /g flag DB<107> $a=4215; $a =~ s/(.)(.)/(sort { $a <=> $b } $1,$2)[0]/eg ;$a => 21 DB<108> $a=4215; $a =~ s/(.)(.)/(sort { $a <=> $b } "$1","$2")[0]/eg + ;$a => 21` [download] Maybe your match part isn't doing what you think it should? Otherwise which Perl version are you using? mine: `$ perl -v This is perl 5, version 14, subversion 2 (v5.14.2) built for i686-linu +x-gnu-thread-multi-64int` [download] Cheers Rolf PS: Je suis Charlie! š) though I agree with others that this approach is overly complicated.	[reply] [d/l] [select]