Programming Practice - Markov Chain Algorithm in Java. Java classes of Markov
chain algorithm. Class Prefix. Class Chain. Class Markov. Prefix Class.
1. Programming Practice - Markov Chain Algorithm in Java Java classes of Markov chain algorithm Class Prefix Class Chain Class Markov Prefix Class class Prefix { public Vector pref; // NPREF adjacent words from input static final int MULTIPLIER = 31; // for hashCode() // Prefix constructor: duplicate existing prefix Prefix(Prefix p) { pref = (Vector) p.pref.clone(); } // Prefix constructor: n copies of str Prefix(int n, String str) { pref = new Vector(); for (int i = 0; i < n; i++) pref.addElement(str); } // Prefix hashCode: generate hash from all prefix words public int hashCode() { int h = 0; for (int i = 0; i < pref.size(); i++) h = MULTIPLIER * h + pref.elementAt(i).hashCode(); return h; } // Prefix equals: compare two prefixes for equal words public boolean equals(Object o) { Prefix p = (Prefix) o; for (int i = 0; i < pref.size(); i++) if (!pref.elementAt(i).equals(p.pref.elementAt(i))) return false; return true; } }
Chain Class class Chain { static final int NPREF = 2; // size of prefix static final String NONWORD = "\n"; // "word" that can't appear Hashtable statetab = new Hashtable(); // key = Prefix, value = suffix Vector Prefix prefix = new Prefix(NPREF, NONWORD); // initial prefix Random rand = new Random(); // Chain build: build State table from input stream void build(InputStream in) throws IOException { StreamTokenizer st = new StreamTokenizer(in); st.resetSyntax(); // remove default rules st.wordChars(0, Character.MAX_VALUE); // turn on all chars st.whitespaceChars(0, ' '); // except up to blank while (st.nextToken() != st.TT_EOF) add(st.sval); add(NONWORD); } // Chain add: add word to suffix list, update prefix void add(String word) { Vector suf = (Vector) statetab.get(prefix); if (suf == null) { suf = new Vector(); statetab.put(new Prefix(prefix), suf); } suf.addElement(word); prefix.pref.removeElementAt(0); prefix.pref.addElement(word); } // Chain generate: generate output words void generate(int nwords) { prefix = new Prefix(NPREF, NONWORD); for (int i = 0; i < nwords; i++) { Vector s = (Vector) statetab.get(prefix); if (s == null) { System.err.println("Markov: internal error: no state"); System.exit(1);
} int r = Math.abs(rand.nextInt()) % s.size(); String suf = (String) s.elementAt(r); if (suf.equals(NONWORD)) break; System.out.println(suf); prefix.pref.removeElementAt(0); prefix.pref.addElement(suf); } } } Markov Class class Markov { static final int MAXGEN = 10000; // maximum words generated public static void main(String[] args) throws IOException { Chain chain = new Chain(); int nwords = MAXGEN; chain.build(System.in); chain.generate(nwords); } }
2. Reading/Writing in Java Reading and Writing Examples (i) The following code illustrates the use of classes Input Stream Reader, Buffered Reader and the method readLine() public static void main(String[] args)throws IOException { … //We construct an input stream is //It allows us to read input text line by line InputStreamReader converter = new InputStreamReader(System.in); BufferedReader is = new BufferedReader(converter); //We prompt the user for N strings //We store input strings inside a String array B String[] B=new String[N]; System.out.println("Enter input strings, one string per line:"); for(int i=0;i 0, a ≥ b //postcondition: i=gcd(a,b) int i,j i:=a j:=b
while j ≠ 0 do compute i=q ∗ j+r, 0 ≤ r < j i:=j j:=r end while return i end function GCD Loop invariant: Q: gcd(i,j)=gcd(a,b) Problem 1: Prepare C++ code for the following test of Example 1:
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Design an integer-valued function with two integer arguments, which implements the loop of Example 1. Design a Boolean valued function Q, which checks whether the invariant holds. In the implementation of Q perform direct calculation of the product. Prepare C++ code for testing your implementation of the loop. Your code should verify whether the invariant holds after the initialization of variables and after every execution of the update. It should prompt the user for two input integers and report the result of the test.
Problem 2: Prepare C++ code for the following test of Euclid’s algorithm:
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Design an integer-valued function with two integer arguments implementing the loop of Example 2. Design a Boolean valued function Q, which checks whether the invariant holds. In the implementation of Q perform direct calculation of the greatest common divisor. Find the largest positive integer (no larger than the smaller of the arguments), which divides both input arguments. Prepare C++ code for testing your implementation of the loop. Your code should verify whether the invariant holds after the initialization of variables and after every execution of the update. It should prompt the user for two input integers and report the result of the test.
