MarkovChainAlgorithm.hpp

include/Partitioning/MarkovChainAlgorithm.hpp

@@ -0,0 +1,73 @@
+#include <time.h>
+#include <iostream>
+#include <string>
+#include <deque>
+#include <map>
+#include <vector>
+
+using namespace std;
+
+const int NPREF = 2;
+const char NONWORD[] = "n";  // cannot appear as real line: we remove newlines
+const int MAXGEN = 10000; // maximum words generated
+
+typedef deque<string> Prefix;
+
+map<Prefix, vector<string> > statetab; // prefix -> suffixes
+
+void    build(Prefix&, istream&);
+void    generate(int nwords);
+void    add(Prefix&, const string&);
+
+// markov main: markov-chain random text generation
+int main(void)
+{
+  int nwords = MAXGEN;
+  Prefix prefix; // current input prefix
+
+  srand(time(NULL));
+  for (int i = 0; i < NPREF; i++)
+    add(prefix, NONWORD);
+  build(prefix, cin);
+  add(prefix, NONWORD);
+  generate(nwords);
+  return 0;
+}
+
+// build: read input words, build state table
+void build(Prefix& prefix, istream& in)
+{
+  string buf;
+
+  while (in >> buf)
+    add(prefix, buf);
+}
+
+// add: add word to suffix deque, update prefix
+void add(Prefix& prefix, const string& s)
+{
+  if (prefix.size() == NPREF) {
+    statetab[prefix].push_back(s);
+    prefix.pop_front();
+  }
+  prefix.push_back(s);
+}
+
+// generate: produce output, one word per line
+void generate(int nwords)
+{
+  Prefix prefix;
+  int i;
+
+  for (i = 0; i < NPREF; i++)
+    add(prefix, NONWORD);
+  for (i = 0; i < nwords; i++) {
+    vector<string>& suf = statetab[prefix];
+    const string& w = suf[rand() % suf.size()];
+    if (w == NONWORD)
+      break;
+    cout << w << "n";
+    prefix.pop_front(); // advance
+    prefix.push_back(w);
+  }
+}