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#!/usr/bin/env perl
use strict;
use warnings;
sub anagrams {
# Tail-recursive with accumulator; iterate over the word accumulating the
# anagrams that can be formed with the already-seen characters
sub iter {
# @acc contains the already computed anagrams
my ($word, @acc) = @_;
if (length($word) == 0) {
# Finished consuming word -> return accumulator
return @acc;
} else {
# Split the current word: first letter vs the rest
my ($head, $tail) = $word =~ /^(.)(.*)$/;
@_ = $tail; # Next word will be the tail of the previous one
# Compute new anagrams by inserting the current letter in all the
# positions of the previous anagrams
foreach my $anagram (@acc) {
for (my $i = 0; $i <= length($anagram); $i++) {
push(@_, $anagram);
substr($_[-1], $i, 0) = $head;
}
}
goto &iter;
}
}
iter(shift, (""));
}
for (@ARGV) {
for (anagrams($_)) {
print $_, "\n";
}
}
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