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#include <algorithm>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <ranges>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
namespace {
void
swap_at_pos(string& str, size_t x, size_t y)
{
if ( str.empty() ) {
return;
}
swap(str.at(x), str.at(y));
}
void
swap_letter(string& str, char x, char y)
{
if ( str.empty() ) {
return;
}
for ( auto& chr: str ) {
if ( chr == x ) {
chr = y;
}
else if ( chr == y ) {
chr = x;
}
}
}
void
rotate_left(string& str, size_t n)
{
if ( str.empty() ) {
return;
}
ranges::rotate(str, str.begin() + static_cast<int>(n % str.size()));
}
void
rotate_right(string& str, size_t n)
{
if ( str.empty() ) {
return;
}
rotate_left(str, str.size() - n);
}
void
rotate(string& str, char chr)
{
if ( str.empty() ) {
return;
}
const auto idx = str.find(chr);
if ( idx == string::npos ) {
return;
}
const auto steps = 1 + idx + (idx >= 4 ? 1 : 0);
rotate_right(str, steps % str.size());
}
void
reverse(string& str, size_t x, size_t y)
{
if ( str.empty() ) {
return;
}
if ( x > y ) {
swap(x, y);
}
reverse(str.begin() + static_cast<string::difference_type>(x),
str.begin() + static_cast<string::difference_type>(y) + 1);
}
void
move(string& str, size_t x, size_t y)
{
if ( str.empty() ) {
return;
}
const auto chr = str.at(x);
str.erase(x, 1);
str.insert(y, 1, chr);
}
vector<string>
readLines(const filesystem::path& filename)
{
ifstream file{ filename };
vector<string> lines;
for ( string line; getline(file, line); ) {
lines.emplace_back(line);
}
return lines;
}
vector<string>
split(const string& line, char sep = ' ')
{
vector<string> words;
stringstream input{ line };
for ( string word; getline(input, word, sep); ) {
words.emplace_back(word);
}
return words;
}
void
part1(const vector<string>& lines, string str)
{
for ( const auto& line: lines ) {
auto words = split(line);
if ( line.starts_with("swap position") ) {
swap_at_pos(str, stoull(words.at(2)), stoull(words.at(5)));
}
else if ( line.starts_with("swap letter") ) {
swap_letter(str, words.at(2).at(0), words.at(5).at(0));
}
else if ( line.starts_with("rotate left") ) {
rotate_left(str, stoull(words.at(2)));
}
else if ( line.starts_with("rotate right") ) {
rotate_right(str, stoull(words.at(2)));
}
else if ( line.starts_with("rotate based") ) {
rotate(str, words.at(6).at(0));
}
else if ( line.starts_with("reverse") ) {
reverse(str, stoull(words.at(2)), stoull(words.at(4)));
}
else if ( line.starts_with("move") ) {
move(str, stoull(words.at(2)), stoull(words.at(5)));
}
else {
cerr << "unknown command: " << line << '\n';
return;
}
}
cout << str << '\n';
}
void
part2(const vector<string>& lines, string str)
{
for ( const auto& line: ranges::reverse_view(lines) ) {
auto words = split(line);
if ( line.starts_with("swap position") ) {
swap_at_pos(str, stoull(words.at(2)), stoull(words.at(5)));
}
else if ( line.starts_with("swap letter") ) {
swap_letter(str, words.at(2).at(0), words.at(5).at(0));
}
else if ( line.starts_with("rotate left") ) {
rotate_right(str, stoull(words.at(2)));
}
else if ( line.starts_with("rotate right") ) {
rotate_left(str, stoull(words.at(2)));
}
else if ( line.starts_with("rotate based") ) {
auto chr = words.at(6).at(0);
for ( size_t i = 0; i != str.size(); ++i ) {
string tmp = str;
rotate_left(tmp, i);
auto idx = tmp.find(chr);
auto steps = (1 + idx + (idx >= 4 ? 1 : 0));
if ( ((steps - i + str.size()) % str.size()) == 0 ) {
str = tmp;
break;
}
}
}
else if ( line.starts_with("reverse") ) {
reverse(str, stoull(words.at(2)), stoull(words.at(4)));
}
else if ( line.starts_with("move") ) {
move(str, stoull(words.at(5)), stoull(words.at(2)));
}
else {
cerr << "unknown command: " << line << '\n';
return;
}
}
cout << str << '\n';
}
} // namespace
int
main()
{
auto lines = readLines("data/day21.txt");
part1(lines, "abcdefgh");
part2(lines, "fbgdceah");
}
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