powerset.cc

#include <algorithm>
#include <iostream>
#include <iterator>
#include <regex>
#include <string>
#include <vector>

using set_t = std::vector<std::string>;

std::vector<set_t> powerset(const set_t &set) {
  std::vector<set_t> result {{}};
  for (const std::string &item : set) {
    std::size_t n = result.size();
    for (std::size_t i = 0; i < n; ++i) {
      set_t rset = result[i];
      rset.push_back(item);
      result.push_back(rset);
    }
  }
  return result;
}

int main() {
  const std::regex token_re("[(),\\s]+");

  while (true) {
    std::string input;
    set_t set;

    std::getline(std::cin, input);
    if (input.length() == 0) {
      break;
    }

    for (auto it = std::sregex_token_iterator(input.begin(), input.end(), token_re, -1);
         it != std::sregex_token_iterator(); ++it) {
      if (it->length() != 0) {
        set.push_back(*it);
      }
    }

    auto pset = powerset(set);
    std::cout << '(';
    for (auto it = pset.begin(); it != pset.end(); ++it) {
      if (it != pset.begin()) {
        std::cout << ' ';
      }
      std::cout << '(';
      for (auto iit = it->begin(); iit != it->end(); ++iit) {
        if (iit != it->begin()) {
          std::cout << ' ';
        }
        std::cout << *iit;
      }
      std::cout << ')';
    }
    std::cout << ')' << std::endl;
  }

  return 0;
}