depth_first_brute_force.cc

#include <iostream>
#include <iterator>
#include <stack>
#include <string>
#include <vector>
class BruteForceIterator
    : public std::iterator<std::input_iterator_tag, std::string> {
 public:
  BruteForceIterator() : length(0), done(true) {}
  BruteForceIterator(int length, const std::vector<std::string>& strings)
      : length(length), strings(strings), done(false) {
    for (std::vector<std::string>::const_reverse_iterator it = strings.rbegin();
         it != strings.rend(); ++it) {
      stack.push(*it);
    }
    ++*this;
  }
  BruteForceIterator& operator++() {
    if (!done) {
      if (!stack.empty()) {
        current_string = stack.top();
        stack.pop();
        if (current_string.size() < length) {
          for (std::vector<std::string>::const_reverse_iterator it =
                   strings.rbegin();
               it != strings.rend(); ++it) {
            stack.push(current_string + *it);
          }
        }
      } else {
        done = true;
      }
    }
    return *this;
  }
  std::string operator*() const { return current_string; }
  bool operator==(const BruteForceIterator& other) const {
    return done == other.done;
  }
  bool operator!=(const BruteForceIterator& other) const {
    return !(*this == other);
  }

 private:
  size_t length;
  std::vector<std::string> strings;
  std::stack<std::string> stack;
  std::string current_string;
  bool done;
};
class BruteForce {
 public:
  BruteForce(int length, const std::vector<std::string>& strings)
      : length(length), strings(strings) {}
  BruteForceIterator begin() { return BruteForceIterator(length, strings); }
  BruteForceIterator end() { return BruteForceIterator(); }

 private:
  int length;
  std::vector<std::string> strings;
};
int main() {
  std::vector<std::string> strings;
  strings.push_back("a");
  strings.push_back("b");
  strings.push_back("c");
  BruteForce brute_force(3, strings);
  for (BruteForceIterator it = brute_force.begin(); it != brute_force.end();
       ++it) {
    std::cout << *it << std::endl;
  }
  return 0;
}