一个编程小题目引发的思考（上）

一个编程小题目引发的思考

首先简介下题目：

输入：一个不超过12位的十进制正整数

输出：打印此数字的十进制计算器表示

例：

输入：145

输出:

      __
||__||__
|   | __|

看到这个题目，也没多想，反正就是把这些数字打出来而已，那就一行一行打呗于是在纸上画了几个计算器表示形式的数字：规律是很明显的，每个数字都由3行4列组成，每一行只有固定的几种样式，比如说8的第一行是" __ "，第二行是"|__|"，第三行是"|__|" 于是就有了思路：只要一位一位的读取这个数字，然后按照上中下的顺序依次打印其计算器表示的三行就行了。由于每个数字的每一行的样式都是固定的，很容易将这些样式抽取出来，经过观察，我找出了其所有的样式，于是就有了如下的代码：

class LCDPrinter
{
    // all the paradigms in the LCD representation
    private static readonly string S0 = "    ";
    private static readonly string S1 = " __ ";
    private static readonly string S2 = "   |";
    private static readonly string S3 = "|   ";
    private static readonly string S4 = " __|";
    private static readonly string S5 = "|__ ";
    private static readonly string S6 = "|__|";
    private static readonly string S7 = "|  |";
    public void PrintNum(int value)
    {
        //TODO: print the number layer by layer
    }
}

接下来的问题就是依次获取一个数的每一位，通过一个递归，很容易实现这个功能：

public void PrintNum(int value)
{
    if (value != 0)
    {
        PrintNum(value / 10, layer);
        Console.Write(value % 10);
    }
}

测试这个方法之后，接下来的工作就是一行一行的打印数值了，按照之前的思路，我把每个数字分为上中下三层，于是可以这么写：

public void PrintNum(int value)
{
    PrintTopBody(value);
    Console.WriteLine();
    PrintMiddleBody(value);
    Console.WriteLine();
    PrintBottomBody(value);
    Console.WriteLine();
}

然后逐个实现每个方法，为了确保这个思路是正确的，先不用考虑所有的数字，只考虑数字1这个情况

private void PrintTopBody(int value)
{
    if (value != 0)
    {
        PrintTopBody(value / 10);
        int num = value % 10;
        switch (num)
        {
            case 1:
                Console.Write(S0);
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }
}
private void PrintMiddleBody(int value)
{
    if (value != 0)
    {
        PrintMiddleBody(value / 10);
        int num = value % 10;
        switch (num)
        {
            case 1:
                Console.Write(S2);
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }
}
private void PrintBottomBody(int value)
{
    if (value != 0)
    {
        PrintBottomBody(value / 10);
        int num = value % 10;
        switch (num)
        {
            case 1:
                Console.Write(S2);
                break;
            default:
                throw new ArgumentOutOfRangeException();
        }
    }
}

然后以1，11，1111作为输入进行测试，发现结果是正确的。接下来就可以完善这三个方法了，经过一段时间的编码和测试，我完成了这道题目。其功能代码如下

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class LCDPriter
{
    private static readonly string S0 = "    ";
    private static readonly string S1 = " __ ";
    private static readonly string S2 = "   |";
    private static readonly string S3 = "|   ";
    private static readonly string S4 = " __|";
    private static readonly string S5 = "|__ ";
    private static readonly string S6 = "|__|";
    private static readonly string S7 = "|  |";
    public void PrintNum(int value)
    {
        PrintTopBody(value);
        Console.WriteLine();
        PrintMiddleBody(value);
        Console.WriteLine();
        PrintBottomBody(value);
        Console.WriteLine();
    }
    private void PrintTopBody(int value)
    {
        if (value != 0)
        {
            PrintTopBody(value / 10);
            int num = value % 10;
            switch (num)
            {
                case 0:
                    Console.Write(S1);
                    break;
                case 1:
                    Console.Write(S0);
                    break;
                case 2:
                    Console.Write(S1);
                    break;
                case 3:
                    Console.Write(S1);
                    break;
                case 4:
                    Console.Write(S0);
                    break;
                case 5:
                    Console.Write(S1);
                    break;
                case 6:
                    Console.Write(S1);
                    break;
                case 7:
                    Console.Write(S1);
                    break;
                case 8:
                    Console.Write(S1);
                    break;
                case 9:
                    Console.Write(S1);
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }
    }
    private void PrintMiddleBody(int value)
    {
        if (value != 0)
        {
            PrintMiddleBody(value / 10);
            int num = value % 10;
            switch (num)
            {
                case 0:
                    Console.Write(S7);
                    break;
                case 1:
                    Console.Write(S2);
                    break;
                case 2:
                    Console.Write(S4);
                    break;
                case 3:
                    Console.Write(S4);
                    break;
                case 4:
                    Console.Write(S6);
                    break;
                case 5:
                    Console.Write(S5);
                    break;
                case 6:
                    Console.Write(S5);
                    break;
                case 7:
                    Console.Write(S2);
                    break;
                case 8:
                    Console.Write(S6);
                    break;
                case 9:
                    Console.Write(S6);
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }
    }
    private void PrintBottomBody(int value)
    {
        if (value != 0)
        {
            PrintBottomBody(value / 10);
            int num = value % 10;
            switch (num)
            {
                case 0:
                    Console.Write(S6);
                    break;
                case 1:
                    Console.Write(S2);
                    break;
                case 2:
                    Console.Write(S5);
                    break;
                case 3:
                    Console.Write(S4);
                    break;
                case 4:
                    Console.Write(S2);
                    break;
                case 5:
                    Console.Write(S4);
                    break;
                case 6:
                    Console.Write(S6);
                    break;
                case 7:
                    Console.Write(S2);
                    break;
                case 8:
                    Console.Write(S6);
                    break;
                case 9:
                    Console.Write(S4);
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }
    }
}