20-Coding-Patterns-DesignGurus.org/11_letter_case_permutation.cpp

/* Problem: https://leetcode.com/problems/letter-case-permutation/
 */

#include "lib_leetcode.h"
#include <iostream>
#include <string>
#include <vector>

std::vector<std::string> solution(const std::string input) {
  std::vector<std::string> perms = {""};
  for (const char c : input) {
    for (std::size_t i = 0, upto = perms.size(); i < upto; i++) {
      if (std::isalpha(c))
        perms.push_back(perms[i] + (char)std::toupper(c));
      perms[i] += std::tolower(c);
    }
  }
  return perms;
}

int main() {
  std::cout << solution("a1b2") << '\n'
            << solution("3z4") << '\n'
            << solution("mQe") << '\n'
            << solution("03fH") << '\n';
}