in reply to Difference between two arrays

I actually got really interested in this problem and thought of trying to use a mathematical formula for what the sum of a sequential numbers is. Anyway, I came up with a solution which I think is elegant, and which uses what I discovered:
```use strict;
use warnings;

my @orig = (1..10);
my @altered = ( [qw( 1  2  3  4  9  5  6  7  8 10)],
[qw( 2  3  4  1  5  6  7  8  9 10)],
[qw( 1  2  3  4 10  5  6  7  8  9)],
[qw( 1  2  3  5  4  6  7  8  9 10)],
[qw( 1  3  4  5  6  7  2  8  9 10)],
[qw( 1  2  3  4  5  6  7  8 10  9)],
[qw( 1  2  3  4  6  5  7  8  9 10)],
);

for my \$test (@altered) {
my %count = ();
my (\$val, \$flag) = (undef, \$orig[0] == \$test->[0]);

for my \$i (0..\$#orig) {
# keep track of what the nums in each array add up to
\$count{before} += \$orig[\$i];
\$count{after}  += \$test->[\$i];

if ((\$flag && (\$count{before} != \$count{after}))
|| (!\$flag && (\$count{before} == \$count{after}))) {
\$val = ( \$test->[\$i] == \$orig[\$i+1])
? \$orig[\$i]
: \$test->[\$i];
last;
}
}
print "\$val moved between (@orig) and (@\$test)\n";
}
```The sum of a sequence of integers from x to x+n equals