113 lines
3.3 KiB
C++
113 lines
3.3 KiB
C++
#include <iostream>
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#include <regex>
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#include <string>
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auto swap_pos(std::string s, std::size_t a, std::size_t b) -> std::string
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{
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std::swap(s.at(a), s.at(b));
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return s;
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}
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auto swap_letters(std::string const& s, char a, char b) -> std::string
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{
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std::string result;
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std::transform(s.begin(), s.end(), std::back_inserter(result), [a, b](char c) {
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if (c == a) {
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return b;
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}
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if (c == b) {
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return a;
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}
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return c;
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});
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return result;
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}
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auto rotate_left(std::string const& s, std::size_t amt) -> std::string
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{
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amt %= s.size();
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return (s + s).substr(amt, s.size());
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}
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auto rotate_right(std::string const& s, std::size_t amt) -> std::string
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{
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amt %= s.size();
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return (s + s).substr(s.size() - amt, s.size());
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}
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auto rotate_on_index(std::string const& s, char c) -> std::string
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{
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auto idx{s.find(c)};
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std::size_t amt{1 + idx + (idx >= 4 ? 1 : 0)};
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return rotate_right(s, amt);
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}
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auto reverse_str(std::string s, std::size_t a, std::size_t b) -> std::string
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{
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std::reverse(s.begin() + a, s.begin() + b + 1);
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return s;
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}
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auto move(std::string s, std::size_t a, std::size_t b) -> std::string
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{
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auto c{s.at(a)};
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s.erase(a, 1);
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s.insert(s.begin() + b, c);
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return s;
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}
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auto main() -> int
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{
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static std::regex swap_pos_re{"swap position (\\d+) with position (\\d+)"};
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static std::regex swap_letter_re{"swap letter (.) with letter (.)"};
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static std::regex rotate_left_re{"rotate left (\\d+) steps?"};
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static std::regex rotate_right_re{"rotate right (\\d+) steps?"};
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static std::regex rotate_based_re{"rotate based on position of letter (.)"};
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static std::regex reverse_re{"reverse positions (\\d+) through (\\d+)"};
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static std::regex move_re{"move position (\\d+) to position (\\d+)"};
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std::string password{"fbgdceah"};
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std::string line;
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std::smatch m;
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std::vector<std::string> commands;
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while (std::getline(std::cin, line)) {
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commands.push_back(line);
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}
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for (auto cmd{commands.rbegin()}; cmd != commands.rend(); ++cmd) {
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if (std::regex_search(*cmd, m, swap_pos_re)) {
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password = swap_pos(password, std::stoul(m.str(1)), std::stoul(m.str(2)));
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}
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else if (std::regex_search(*cmd, m, swap_letter_re)) {
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password = swap_letters(password, m.str(1)[0], m.str(2)[0]);
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}
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else if (std::regex_search(*cmd, m, rotate_left_re)) {
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password = rotate_right(password, std::stoul(m.str(1)));
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}
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else if (std::regex_search(*cmd, m, rotate_right_re)) {
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password = rotate_left(password, std::stoul(m.str(1)));
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}
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else if (std::regex_search(*cmd, m, rotate_based_re)) {
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/* This is the only reverse command whose inverse is not obvious to me. So just do repeated
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* rotations until we get to one which works.
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*/
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std::string trial{password};
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while (rotate_on_index(trial, m.str(1)[0]) != password) {
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trial = rotate_left(trial, 1);
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};
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password = trial;
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}
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else if (std::regex_search(*cmd, m, reverse_re)) {
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password = reverse_str(password, std::stoul(m.str(1)), std::stoul(m.str(2)));
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}
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else if (std::regex_search(*cmd, m, move_re)) {
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password = move(password, std::stoul(m.str(2)), std::stoul(m.str(1)));
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}
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else {
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std::cerr << "Unable to interpret " << *cmd << "\n";
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return 1;
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}
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std::cout << *cmd << " -> " << password << '\n';
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}
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std::cout << password << '\n';
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} |