Implement an algorithm to print all valid combinations of n-pairs of parentheses.

CC150-9.6.java

package POJ;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class Main {

	/**
	 * 
	 * 9.6 Implement an algorithm to print all valid combinations of n-pairs of parentheses.
	 * 
	 * 
	 */
	public List<String> getParentheses(int n) {
		List<String> result = new ArrayList<String>();
		if (n <= 0)
			return result;
		getResult(result, n, 0, 0, "");
		return result;
	}

	private void getResult(List<String> result, int n, int positive,
			int negative, String temp) {
		// TODO Auto-generated method stub
		if (negative > positive)
			return;
		if (negative + positive == 2 * n) {
			if (positive == negative)
				result.add(temp);
			return;
		}
		getResult(result, n, positive + 1, negative, temp + "(");
		getResult(result, n, positive, negative + 1, temp + ")");
	}
}