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my $modified = reduce{
    my( $x1, $y1, $x2, $y2 ) = ( @{ @{ $a }[ -1 ] }, @$b );
     $x2 < $x1 ? pop @{ $a } : push @{ $a }, $b;
    $a;
} [ shift @points ], @points;

my $i = 1;
while ($i < @points) {
...
        $i++;
    }
}

my $modified = [];
for my $point (@points) {
...
        push @$modified, $point;
    }
}

my @m;
@m&&$m[-1][0]>$_->[0]?pop @m:push @m,$_ for @points;