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#include <array>
#include <iostream>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
namespace {
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
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;
}
}
}
vector<uint8_t>
knothash(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);
vector<uint8_t> result;
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);
}
result.emplace_back(value & 0xFF);
}
return result;
}
void
part1(const string& line)
{
int count = 0;
for ( int i = 0; i != 128; ++i ) {
auto result = knothash(line + "-"s + to_string(i));
for ( const auto value: result ) {
count += popcount(value);
}
}
cout << "Part1: " << count << '\n';
}
void
part2(const string& line)
{
set<tuple<size_t, size_t>> grid;
for ( size_t y = 0; y != 128; ++y ) {
auto result = knothash(line + "-"s + to_string(y));
for ( size_t x = 0; x != 128; ++x ) {
auto value = result.at(x / 8);
auto mask = 1u << (7 - (x % 8));
if ( (value & mask) != 0 ) {
grid.emplace(x, y);
}
}
}
int count = 0;
for ( size_t x = 0; x != 128; ++x ) {
for ( size_t y = 0; y != 128; ++y ) {
if ( !grid.contains({ x, y }) ) {
continue;
}
++count;
queue<tuple<size_t, size_t>> queue;
queue.emplace(x, y);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
grid.erase(pos);
static array<tuple<size_t, size_t>, 4> dirs{ make_tuple(-1, 0), make_tuple(1, 0), make_tuple(0, -1), make_tuple(0, 1) };
for ( const auto [dx, dy]: dirs ) {
const auto new_pos = make_tuple(dx + get<0>(pos), dy + get<1>(pos));
if ( grid.contains(new_pos) ) {
queue.emplace(new_pos);
}
}
}
}
}
cout << "Part2: " << count << '\n';
}
} // namespace
int
main()
{
const string input = "ffayrhll";
part1(input);
part2(input);
}
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