use List::Util qw[ reduce ];
my @in = ( 41888, 41889, 41890, 41892, 41895 );
my @missing;
reduce{ push @missing, $a+1 .. $b-1; $b } @in;
print @missing;

41891 41893 41894

[download]

If your list is large, then this will be more (memory) efficient: 

my @in = ( 41888, 41889, 41890, 41892, 41895 );
my @missing;
push @missing, $in[ $_ ] +1 .. $in[ $_+1 ] -1 for 0 .. $#in-1;
print @missing;

41891 41893 41894

[download]
Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail
"Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon

In reply to Re: Finding missing numbers in a list by BrowserUk
in thread Finding missing numbers in a list by Morlane

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