adventofcode/2023/09/Part2.pm

use 5.38.0;

package Part2;

use Part1;

use List::AllUtils qw/ all sum /;

sub predict(@entries) {
    my $sum = 0;

    my @first = ();

    until( all { !$_ } @entries ) {
        push @first, $entries[0];
        @entries = map { $entries[$_]-$entries[$_-1] } 1..$#entries;
    }

    while(@first) {
        $sum = pop( @first ) - $sum;
    }

    return $sum;
}

sub solution_2 ($input) {
    my @lines = map { [split]} split "\n", $input;

    return sum  map { predict(@$_) } @lines;
}

1;