有10阶梯, 每次走1,2 or 3 阶,有多少种方式???

/**
 * 有10阶梯, 每次走1,2 or 3 阶,有多少种方式???
 */
public class Test
{
    static final int s = 10; 

    static int len = 0, sum = 0;

    static int step[] = new int[s];

    static void compute(final int stair)
    {
        // get result
        if (stair == 0)
        {
            printSum();
            sum++;
            return;
        }
        // 步数 1,2 or 3 阶
        for (int i = 1; i < 4; i++)
        {
            step[len] = i;
            len++;
            compute(stair - i);
            len--;
        }
    }

    static void printSum()
    {
        for (int i = 0; i < len; i++)
            System.out.print(step[i] + " ");
        System.out.println();
    }

    public static void main(String args[])
    {
        compute(s);
        System.out.println(sum );
    }
}