#algorithm# Given the number, print all pairs of '(' and ')'

printBrackets.pl

use strict;
use warnings;

my @output;
sub printBrackets($$)
{
	my ($nLeft, $nRight) = @_;
	# recursion end condition
	if($nLeft == 0 && $nRight == 0)
	{
		print join "", @output;
		print "\n";
		return;
	}
	
	# in any time, existing left brackets must >= right brackets
	if($nLeft == $nRight)
	{
		push @output, "(";
		printBrackets($nLeft-1, $nRight);
		pop @output;
	}
	else
	{
		if($nLeft > 0)
		{
			push @output, "(";
			printBrackets($nLeft-1, $nRight);
			pop @output;
		}
		if($nRight > 0)
		{
			push @output, ")";
			printBrackets($nLeft, $nRight-1);
			pop @output;
		}
	}
}

printBrackets(1,1);
printBrackets(2,2);
printBrackets(3,3);

perl，其实很美