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/**

* Practiced on 12/4/2012

*

* Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

* For example, given n = 3, a solution set is:

* "((()))", "(()())", "(())()", "()(())", "()()()"

*/

package com.congli.leetcode;

import java.util.ArrayList;

public class GenerateParenthesis {

public ArrayList<String> generateParenthesis(int n)

{

ArrayList<String> result = new ArrayList<String>();

helper(result, 0, 0, n, new char[2*n]);

return result;

}

private void helper(ArrayList<String> result, int leftNum, int rightNum, int n, char[] str)

{

if(leftNum == n && rightNum == n)

{

result.add(new String(str));

return;

}

if(leftNum < n)

{

str[leftNum+rightNum] = '(';

helper(result, leftNum+1, rightNum, n, str);

}

if(rightNum < leftNum)

{

str[leftNum+rightNum] = ')';

helper(result, leftNum, rightNum+1, n, str);

}

}

}