Generate Parentheses

public class Solution {
    public ArrayList<String> res;

	public ArrayList<String> generateParenthesis(int n) {
		// Start typing your Java solution below
		// DO NOT write main() function
		res = new ArrayList<String>();
		generate(0, 0, n, "");
		return res;
	}

	public void generate(int left, int right, int n, String temp) {
		if (right == n) {
			res.add(temp);
		}
		if (left < n)
			generate(left + 1, right, n, temp + "(");
		if (right < left)
			generate(left, right + 1, n, temp + ")");
	}
}