打印从1到最大的n位数（Java实现）

public class E17Print1ToMax {
    //打印从1到最大的n位数
    //用字符数组解决大数问题

    public static void print1ToMaxN_Solution1(int n){
        //循环实现
        if (n <= 0)
            return;
        //初始化,索引0处存放个位数
        char[] bits = new char[n + 1];
        for (int i = 0; i <= n; i ++)
            bits[i] = '0';
        //当第n+1位没有进位时打印
        while(bits[n] == '0'){
            printNumber(bits, n);
            //将数字加1
            addNumber(bits, n);
        }

    }

    private static void addNumber(char[] bits, int n){
        for (int i = 0; i <= n; i++){
            //避免进位时char类型越界，将该位数字保存到int类型中
            int number = bits[i] - '0';
            number++;
            if (number >= 10){ //进位
                bits[i] = '0';
            }
            else{ //不能进位时跳出循环
                bits[i] += 1;
                break;
            }
        }
    }

    private static void printNumber(char[] bits, int n){
        //从第一个不为0的位开始打印
        StringBuilder number = new StringBuilder();
        for (int i = n - 1; i >= 0; i--){
            if (bits[i] != '0'){
                while(i >= 0){
                    number.append(bits[i]);
                    i--;
                }
            }
        }
        System.out.print(number + "\n");
    }

    public static void print1ToMaxN_Solution2(int n){
        //递归实现，全排列
        if (n <= 0)
            return;
        //初始化,索引0处存放个位数
        char[] bits = new char[n];
        for (int i = 0; i < n; i ++)
            bits[i] = '0';
        //排列
        for (int i = 0; i < 10; i++){
            bits[n - 1] = (char) (i + '0');
            print1ToMaxNCore(bits, n, n - 2);
        }
    }

    private static void print1ToMaxNCore(char[] bits, int n, int index){
        //每次递归结束时打印数字
        if (index == -1){
            printNumber(bits, n);
            return;
        }
        for (int i = 0; i < 10; i++){
            bits[index] = (char) (i + '0');
            print1ToMaxNCore(bits, n, index - 1);
        }
    }

    //测试用例
    public static void main(String[] args){
        char[] c = {'9', '1', '0', '3', '1', '0', '0', '0',};
        E17Print1ToMax.printNumber(c, 8);

        E17Print1ToMax.print1ToMaxN_Solution1(6);
        E17Print1ToMax.print1ToMaxN_Solution2(6);
    }
}