C# I/O 助手类

在使用 C# 语言解 ACM 题的时候，如果能够有一个 ReadInt32 方法直接从标准输入读取整数比较方便的。下面就是一个 I/O 助手类 IOHelper：

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namespace Skyiv {   using System;   using System.IO;   using System.Text;     sealed class IOHelper : IDisposable   {     static readonly Encoding Encoding = Encoding.ASCII; // or UTF8 ?     static readonly byte[] EOLS = Encoding.GetBytes(Environment.NewLine);     static readonly byte[] BLANKS = { 9, 10, 13, 32 }; // tab,lf,cr,space     static readonly byte EOF = 0; // assume '\0' not in input file           byte[] buf = new byte[32]; // for Write(int n)     byte[] buffer = new byte[64 * 1024];     int current = 0;     int count = 0;     BinaryReader reader;     BinaryWriter writer;           public IOHelper()       : this(Console.OpenStandardInput(), Console.OpenStandardOutput())     {}           public IOHelper(Stream reader, Stream writer)     {       this.reader = new BinaryReader(reader);       this.writer = new BinaryWriter(writer);     }           byte ReadByte()     {       if (current >= count)       {         count = reader.Read(buffer, current = 0, buffer.Length);         if (count == 0) return EOF;       }       return buffer[current++];     }           public static byte[] GetBytes(string str)     {       return Encoding.GetBytes(str);     }           public int ReadInt32()     {       var n = 0;       var ok = false;       for (byte b; (b = ReadByte()) != EOF; )       {         if (Array.IndexOf(BLANKS, b) >= 0)           if (ok) break;           else continue;         n = n * 10 + (b - '0');         ok = true;       }       return n;     }           public int ReadLine(byte[] buffer)     {       var n = 0;       while (n < buffer.Length)       {         var b = ReadByte();         if (b == EOLS[0])         {           if (EOLS.Length == 2 && ReadByte() != EOLS[1])             throw new InvalidDataException("Invalid EOL");           break;         }         buffer[n++] = b;       }       return n;     }       public void Write(int n)     {       if (n == 0) { writer.Write((byte)'0'); return; }       var i = buf.Length;       for (; n > 0; n /= 10) buf[--i] = (byte)((n % 10) + '0');       Write(buf, i, buf.Length - i);     }           public void Write(byte[] buffer, int index, int count)     {       writer.Write(buffer, index, count);     }           public void Write(string str)     {       var buffer = Encoding.GetBytes(str);       writer.Write(buffer, 0, buffer.Length);     }           public void WriteSpace()     {       writer.Write(BLANKS, 3, 1);     }           public void WriteLine()     {       writer.Write(EOLS, 0, EOLS.Length);     }           public void Dispose()     {       if (reader != null) reader.Close();       if (writer != null) writer.Close();     }   } }

此外，IOHelper 类还提供以下方法用于处理字符串：

• public int ReadLine(byte[] buffer)
• public void Write(byte[] buffer, int index, int count)

类似于 C/C++ 语言，这两个方法仅仅把字符串当作字节数组处理，使用 ASCII 码。而不是象 C# 语言中字符串是使用 Unicode 进行编码。

下面是一个使用示例，题目来源请参见“I-Keyboard”这篇随笔。

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namespace Skyiv.Ben.Acm {   using System;     // http://www.spoj.pl/problems/IKEYB/   sealed class Ikeyb   {     const int MAX = 90;           static int[,] cost = new int[MAX + 1, MAX + 1];     static int[,] price = new int[MAX + 1, MAX + 1];     static int[,] index = new int[MAX + 1, MAX + 1];     static int[] F = new int[MAX];     static byte[] keys = new byte[MAX];     static byte[] letters = new byte[MAX];     static byte[] message1 = IOHelper.GetBytes("Keypad #");     static byte[] message2 = IOHelper.GetBytes(": ");           static IOHelper helper;       static void Main()     {       using (helper = new IOHelper())       {         var runner = new Ikeyb();         var T = helper.ReadInt32();         for (var n = 1; n <= T; n++) runner.Run(n);       }     }       void Run(int n)     {       var K = helper.ReadInt32();       var L = helper.ReadInt32();       helper.ReadLine(keys);       helper.ReadLine(letters);       for (var i = 0; i < L; i++) F[i] = helper.ReadInt32();       Initialize(K, L);       Compute(K, L);       helper.Write(message1, 0, message1.Length);       helper.Write(n);       helper.Write(message2, 0, 1);       helper.WriteLine();       Output(K, L);       helper.WriteLine();     }           void Initialize(int K, int L)     {       for (var i = 0; i <= K; i++)         for (var j = 1; j <= L; j++)           price[i, j] = int.MaxValue / 2;       for (var i = 1; i <= L; i++)         for (var j = i; j <= L; j++)           cost[i, j] = cost[i, j - 1] + (j - i + 1) * F[j - 1];     }           void Compute(int K, int L)     {       for (var i = 1; i <= K; i++)         for (var j = i; j <= L; j++)           for (var n = 1; n <= j - i + 1; n++)           {             var sum = price[i - 1, j - n] + cost[j - n + 1, j];             if (sum <= price[i, j])             {               price[i, j] = sum;               index[i, j] = n;             }           }     }       void Output(int K, int L)     {       if (K == 0) return;       var n = index[K--, L];       Output(K, L - n);       helper.Write(keys, K, 1);       helper.Write(message2, 0, message2.Length);       helper.Write(letters, L - n, n);       helper.WriteLine();     }   } }

如果给出以下输入：

1
2 5
*#
ABCDE
1024
32768
2147483647
987
654321

上述程序将产生以下输出：

Keypad #1:
*: ABCD
#: E

注意上述输出其实是有问题的，正确的输出应该分为 AB 和 CDE 两组。但是程序本身是没有问题的，而是输入数据有问题。因为原来的题目中限定各个字母出现的频率不能超过 100000。