##!/usr/bin/env perl6

sub parens( $s ) {
	return $s eq '9' ?? $s !! '(' ~ $s ~ ')';
};

sub operate( $num1, $exp1, $num2, $exp2 ) {
	my @result;
	
	push @result, $num1 + $num2;
	push @result, parens( $exp1 ) ~ " + " ~ parens( $exp2 );

	push @result, $num1 - $num2;
	push @result, parens( $exp1 ) ~ " - " ~ parens( $exp2 );

	push @result, $num1 * $num2;
	push @result, parens( $exp1 ) ~ " * " ~ parens( $exp2 );

	if $num2 != 0 {
		push @result, $num1 / $num2;
		push @result, parens( $exp1 ) ~ " / " ~ parens( $exp2 );

		push @result, $num1 % $num2;
		push @result, parens( $exp1 ) ~ " % " ~ parens( $exp2 );
	}

	return @result;
}

sub mate-levels( %numexp1, %numexp2 ) {
	my @result;

	for %numexp1.kv -> $num1, $exp1 {
		for %numexp2.kv -> $num2, $exp2 {
			push @result, operate $num1, $exp1, $num2, $exp2;
			push @result, operate $num2, $exp2, $num1, $exp1;
		}
	}
	return @result;
}

sub insert-num-exp-pairs( %dst, @new ) {
	for @new -> $num, $exp {
		# Select the most readable (=shortest) expression.
		if not %dst.exists( $num ) or %dst{$num}.chars > $exp.chars {
			%dst{$num} = $exp;
		}
	}
}

sub MAIN ( Int $N ) {
	# @all[1] holds numbers and expressions built with 1 nine.
	# @all[2..4] will hold numbers and expressions built with 2..4 nines.
	my @all = ( 
		{},
		{ 9 => "9", -9 => "-9" },
		{},
		{},
		{}
	);

	insert-num-exp-pairs( @all[2], mate-levels( @all[1], @all[1] ));

	insert-num-exp-pairs( @all[3], mate-levels( @all[1], @all[2] ));

	insert-num-exp-pairs( @all[4], mate-levels( @all[1], @all[3] ));
	insert-num-exp-pairs( @all[4], mate-levels( @all[2], @all[2] ));

	for 0 .. $N -> $n {
		say $n ~ ( @all[4].exists( $n ) ?? ' = ' ~ @all[4]{$n} !! '' );
	};
}