测试一下markdown

这是二级标题

以后就在这里写文章啦。
加粗
倾斜

public class BackTrack {
    public static void main(String[] args) {
        int n = 2;
        int leftnum = n, rightnum = n;//左括号和右括号都各有n个
        ArrayList<String> results = new ArrayList<String>();//用于存放解空间
        parentheses("", results, leftnum, rightnum);
        for (String s : results)
            System.out.println(s);
    }

    public static void parentheses(String sublist, ArrayList<String> results, int leftnum, int rightnum) {
        if (leftnum == 0 && rightnum == 0)//结束
            results.add(sublist);
        if (rightnum > leftnum)//选择和条件。对于不同的if顺序，输出的结果顺序是不一样的，但是构成一样的解空间
            parentheses(sublist + ")", results, leftnum, rightnum - 1);
        if (leftnum > 0)
            parentheses(sublist + "(", results, leftnum - 1, rightnum);
    }
}