My code below works if I compile it on online perl compiler.
But it does not work on Hackerrank.
I am pretty sure it is related with the input/output format, which I do not know how to fix.
In my code, I assume the input is just a list of integer.
I have read about other problems related with stdin/out in this forum, but since i am a beginner, I cannot understand the discussion.

Problem : findPoint

sub findPoint {
# Write your code here
# my ($n, $px, $py, $qx, $qy) = @_;
my $m = scalar(@_);
my $px = 0;
my $py = 0;
my $qx = 0;
my $qy = 0; 
my $rx = 0;
my $ry = 0;  

for (my $i = 0; $i < $_[0]; $i++){
        $px = $_[$i*4 + 1];
        $py = $_[$i*4 + 2];
        $qx = $_[$i*4 + 3];
        $qy = $_[$i*4 + 4];
        
        $rx = 2*$qx - $px;
        $ry = 2*$qy - $py;
        print "$rx $ry n";
}

}

findPoint( 2, 0, 0, 1, 1, 1, 1, 2, 2)

format from Hackerrank.
enter image description here
enter image description here

I tried to compile it on online perl compiler and it works.