QuestionB.java

package Question9_6;

import java.util.ArrayList;

public class QuestionB {
	
	public static void addParen(ArrayList<String> list, int leftRem, int rightRem, char[] str, int count) {
		if (leftRem < 0 || rightRem < leftRem) return; // invalid state
		
		if (leftRem == 0 && rightRem == 0) { /* all out of left and right parentheses */
			String s = String.copyValueOf(str);
			list.add(s);
		} else {
			if (leftRem > 0) { // try a left paren, if there are some available
				str[count] = '(';
				addParen(list, leftRem - 1, rightRem, str, count + 1);
			}
			if (rightRem > leftRem) { // try a right paren, if there�s a matching left
				str[count] = ')';
				addParen(list, leftRem, rightRem - 1, str, count + 1);
			}
		}
	}
	
	public static ArrayList<String> generateParens(int count) {
		char[] str = new char[count*2];
		ArrayList<String> list = new ArrayList<String>();
		addParen(list, count, count, str, 0);
		return list;
	}
	
	public static void main(String[] args) {
		ArrayList<String> list = generateParens(3);
		for (String s : list) {
			System.out.println(s);
		}
		System.out.println(list.size());		
	}

}