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#include <filesystem>
#include <fstream>
#include <iostream>
#include <numeric>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
namespace {
string
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
string line;
getline(file, line);
return line;
}
vector<size_t>
split(const string& line)
{
stringstream strm{ line };
vector<size_t> data;
for ( string word; getline(strm, word, ','); ) {
data.emplace_back(stoul(word));
}
return data;
}
vector<unsigned>
gen_data(size_t len)
{
vector<unsigned> data(len);
iota(data.begin(), data.end(), 0UL);
return data;
}
void
reverse(vector<unsigned>& data, size_t start, size_t len)
{
auto end = start + len;
while ( start < end ) {
swap(data.at(start++ % data.size()), data.at(--end % data.size()));
}
}
void
hash(vector<unsigned>& data, const vector<size_t>& lengths)
{
size_t pos = 0;
for ( size_t skip = 0; skip != lengths.size(); ++skip ) {
reverse(data, pos, lengths.at(skip));
pos += lengths.at(skip) + skip;
}
}
void
part1(size_t len, const string& line)
{
auto data = gen_data(len);
auto lengths = split(line);
hash(data, lengths);
cout << "Part1: " << data.at(0) * data.at(1) << '\n';
}
void
hash64(vector<unsigned>& data, const vector<size_t>& lengths)
{
size_t pos = 0;
size_t skip = 0;
for ( size_t i = 0; i != 64; ++i ) {
for ( auto length: lengths ) {
reverse(data, pos, length);
pos += length + skip;
++skip;
}
}
}
void
part2(string line)
{
line += char(17);
line += char(31);
line += char(73);
line += char(47);
line += char(23);
vector<size_t> lengths;
for ( const auto byte: line ) {
lengths.emplace_back(static_cast<unsigned char>(byte));
}
auto data = gen_data(256);
hash64(data, lengths);
cout << "Part2: ";
for ( size_t i = 0; i != 256; i += 16 ) {
size_t value = 0;
for ( size_t j = 0; j != 16; ++j ) {
value ^= data.at(i + j);
}
cout << setw(2) << setfill('0') << hex << (value & 0xFF);
}
cout << '\n';
}
} // namespace
int
main()
{
auto line = read_file("data/day10.txt");
part1(256, line);
part2(line);
}
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