「プログラミング作法」The Practice of Programming MarkovChainのC#実装例(Generics不使用)

mc.cs

/* PoP 3 Markov Chain in C# */
/* 2003/02/17: suchi -- */

using System;
using System.IO;
using System.Collections;
using System.Text.RegularExpressions;

class Prefix {
    const int MULTIPLIER = 31;   // for hashcode
    public ArrayList pref;
    //
    public Prefix(Prefix p)    // copy ctor
    {
        pref = (ArrayList)p.pref.Clone();
    }
    public Prefix(int n, String str)
    {
        pref = new ArrayList();
        for (int i = 0; i < n; i++) {
            pref.Add(str);
        }
    }
    // compare prefix
    public override bool Equals(Object o)
    {
        Prefix p = (Prefix)o;
        for (int i = 0; i < pref.Count; i++) {
            if (!pref[i].Equals(p.pref[i])) {
                return false;
            }
        }
        return true;
    }

    public override int GetHashCode()
    {
        int h = 0;
        for (int i = 0; i < pref.Count; i++) {
            h = MULTIPLIER * h + pref[i].GetHashCode();
        }

        return h;
    }

}

class Chain {
    const int NPREF = 2;
    const String NONWORD = "\n";
    Hashtable statetab = new Hashtable();
    Prefix prefix = new Prefix(NPREF, NONWORD);
    Random rand = new Random();
    //
    public void build(TextReader sr)
    {
        Regex rex = new Regex("[ \t]+");
        String line;
        while (sr.Peek() > -1) {
            line = sr.ReadLine();
            String[] fields = rex.Split(line);
            for (int i = 0; i < fields.Length; ++i) {
                add(fields[i]);
            }
        }
        add(NONWORD);
    }
    public void add(String word)
    {
        ArrayList suf = (ArrayList)statetab[prefix];
        if (suf == null) {
            suf = new ArrayList();
            Prefix p = new Prefix(prefix);
            statetab[p] = suf;
        }
        suf.Add(word);
        prefix.pref.RemoveAt(0);
        prefix.pref.Add(word);
    }

    public void generate(int nwords)
    {
        prefix = new Prefix(NPREF, NONWORD);
        for (int i = 0; i < nwords; i++) {
            ArrayList s = (ArrayList)statetab[prefix];
            int r = rand.Next() % s.Count;
            String suf = (String)s[r];
            if (suf.Equals(NONWORD)) {
                break;  // for(i)
            }
            Console.WriteLine(suf);
            prefix.pref.RemoveAt(0);
            prefix.pref.Add(suf);
        }
    }
}

class Markov {
    const int MAXGEN = 10000;
    public static void Main(String[] args)
    {
        Chain chain = new Chain();
        int nwords = MAXGEN;
        chain.build(Console.In);
        chain.generate(nwords);
    }
}