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// Standard C++
#include <algorithm>
#include <array>
#include <iostream>
#include <map>
#include <queue>
#include <string>
#include <tuple>
// System
#include <md5.h>
using namespace std;
namespace {
using pos_type = tuple<int, int, string>;
string
md5(string_view input)
{
array<char, MD5_DIGEST_STRING_LENGTH> digest{};
MD5Data(input.data(), input.size(), digest.data());
return digest.data();
}
void
part1(const string& passcode)
{
static const map<size_t, tuple<char, int, int>> dirs{
{ 0, { 'U', 0, -1 } },
{ 1, { 'D', 0, 1 } },
{ 2, { 'L', -1, 0 } },
{ 3, { 'R', 1, 0 } }
};
auto is_open = [](auto chr) {
return strchr("bcdef", chr) != nullptr;
};
queue<pos_type> queue;
queue.emplace(0, 0, "");
while ( !queue.empty() ) {
auto [x, y, path] = queue.front();
queue.pop();
if ( x == 3 && y == 3 ) {
cout << path << '\n';
return;
}
auto hash = md5(passcode + path);
for ( size_t i = 0; i != 4; ++i ) {
if ( !is_open(hash.at(i)) ) {
continue;
}
auto [chr, dx, dy] = dirs.at(i);
auto new_x = x + dx;
auto new_y = y + dy;
if ( new_x < 0 || new_y < 0 || new_x >= 4 || new_y >= 4 ) {
continue;
}
queue.emplace(new_x, new_y, path + chr);
}
}
}
void
part2(const string& passcode)
{
static const map<size_t, tuple<char, int, int>> dirs{
{ 0, { 'U', 0, -1 } },
{ 1, { 'D', 0, 1 } },
{ 2, { 'L', -1, 0 } },
{ 3, { 'R', 1, 0 } }
};
auto is_open = [](auto chr) {
return strchr("bcdef", chr) != nullptr;
};
size_t max_length = 0;
queue<pos_type> queue;
queue.emplace(0, 0, "");
while ( !queue.empty() ) {
auto [x, y, path] = queue.front();
queue.pop();
if ( x == 3 && y == 3 ) {
max_length = max(max_length, path.size());
continue;
}
auto hash = md5(passcode + path);
for ( size_t i = 0; i != 4; ++i ) {
if ( !is_open(hash.at(i)) ) {
continue;
}
auto [chr, dx, dy] = dirs.at(i);
auto new_x = x + dx;
auto new_y = y + dy;
if ( new_x < 0 || new_y < 0 || new_x >= 4 || new_y >= 4 ) {
continue;
}
queue.emplace(new_x, new_y, path + chr);
}
}
cout << max_length << '\n';
}
} // namespace
int
main()
{
part1("awrkjxxr");
part2("awrkjxxr");
}
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