gistfile1.txt

#include <iostream>
#include <random>
#include <functional>
#include <map>

namespace {

bool enumerate;

std::random_device rd;
std::mt19937 mt(rd());

typedef std::vector<std::function<std::string()>> FuncVec;

std::vector<int> choices, maxChoices;
unsigned depth;

const bool advance() {
  do {
    depth--;
    if (choices.at(depth) < (maxChoices.at(depth) - 1)) {
      choices.at(depth)++;
      return true;
    }
    choices.pop_back();
    maxChoices.pop_back();
  } while (depth > 0);
  return false;
}

const std::string choose(const FuncVec &v) {
  if (enumerate) {
    ++depth;
    if (depth > choices.size()) {
      choices.push_back(0);
      maxChoices.push_back(v.size());
    }
    return v.at(choices.at(depth - 1))();
  } else {
    std::uniform_int_distribution<> chooseN(0, v.size() - 1);
    return v.at(chooseN(mt))();
  }
}

const std::string EF() {
  return choose(FuncVec {
    []() { return "E"; },
    []() { return "F"; }
    });
}

const std::string D() {
  return choose(FuncVec {
    []() { return "D"; },
    []() { return EF(); }
    });
}

const std::string C() {
  return choose(FuncVec {
    []() { return "C"; },
    []() { return D(); }
    });
}

const std::string B() {
  return choose(FuncVec {
    []() { return "B"; },
    []() { return C(); }
    });
}

const std::string A() {
  return choose(FuncVec {
    []() { return "A"; },
    []() { return B(); }
    });
}

[[ noreturn ]] void usage() {
  std::cout << "silly-fuzz enumerate|random\n";
  exit(-1);
}

} // namespace

int main(int argc, char *argv[]) {
  if (argc != 2)
    usage();
  if (((std::string)argv[1]).compare("enumerate") == 0)
    enumerate = true;
  else if (((std::string)argv[1]).compare("random") == 0)
    enumerate = false;
  else
    usage();
  if (enumerate) {
    do {
      depth = 0;
      std::cout << A() << "\n";
    } while (advance());
  } else {
    std::map<std::string, int> m;
    const int N = 10000000;
    for (int i = 0; i < N; i++) {
      auto s = A();
      auto it = m.find(s);
      if (it == m.end())
        m.insert({s, 1});
      else
        ++it->second;
    }
    for (auto it : m)
      std::cout << it.first << " " << ((double)100 * it.second / N) << "\n";
  }
}