sub mandist { my($x1, $y1, $x2, $y2) = @_; abs( $x1 - $x2 ) + abs( $y1 - $y2 ) }

sub f {
    my($x, $y, @p) = @_;
    my $i = 0;
    (
      map  { $$_{index}                                                 }
      sort { $$a{mandist} <=> $$b{mandist} || $$a{index} <=> $$b{index} }
      map  { $$_{mandist} = mandist( $x, $y, @$_{qw(px py)} ); $_       }
      grep { $$_{px} == $x or $$_{py} == $y                             }
      map  { {px => $$_[0], py => $$_[1], index => $i++}                }
      @p
    )[0] // -1

}

print pop(@$_) == f(@$_) ? "ok\n" : "err\n" for
[ 3,  4    => [1, 2], [3, 1], [2, 4], [2, 3]  =>  2 ],
[ 2,  5    => [3, 4], [2, 3], [1, 5], [2, 5]  =>  3 ],
[ 1,  1    => [2, 2], [3, 3], [4, 4]          => -1 ],
[ 0,  0    => [0, 1], [1, 0], [0, 2], [2, 0]  =>  0 ],
[ 5,  5    => [5, 6], [6, 5], [5, 4], [4, 5]  =>  0 ],