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#include <bits/stdc++.h>
namespace views = std::views;
namespace ranges = std::ranges;
void pad_grid(std::vector<std::string>& input) {
for (size_t i = 0; i < input.size(); ++i) {
input[i] = "." + input[i] + ".";
}
int const row_size = input[0].size();
input.emplace(input.begin(), row_size, '.');
input.emplace_back(row_size, '.');
}
auto parse_input(std::istream& is) {
const std::string input = {
std::istreambuf_iterator<char>(is),
std::istreambuf_iterator<char>()
};
auto lines = views::split(input, '\n')
| views::filter([](auto&& line) { return not line.empty(); })
| ranges::to<std::vector<std::string>>();
pad_grid(lines);
return lines;
}
constexpr std::array<char, 3> tuple_to_array(std::tuple<char, char, char>&& t) {
return {std::get<0>(t), std::get<1>(t), std::get<2>(t)};
}
auto next_state(std::vector<std::string> const& input) {
int nremoved = 0;
auto forklift_pass = [&nremoved](auto&& columns) -> char {
if (columns[1][1] == '@' and ranges::count(columns | views::join, '@') < 5) {
++nremoved;
return '.';
}
return columns[1][1];
};
std::vector<std::string> next_state;
for (auto const& rows : input | views::slide(3)) {
next_state.push_back(
views::zip(rows[0], rows[1], rows[2])
| views::transform(tuple_to_array)
| views::slide(3)
| views::transform(forklift_pass)
| ranges::to<std::string>());
}
pad_grid(next_state);
return std::make_tuple(next_state, nremoved);
}
void part1(auto input) {
auto const [_, answer] = next_state(input);
std::println("{}", answer);
}
void part2(auto input) {
// Write second part solution here
int answer = 0;
while (true) {
auto const [_next_state, increment] = next_state(input);
if (increment == 0) {
break;
}
input = _next_state;
answer += increment;
}
std::println("{}", answer);
}
int main() {
auto input = parse_input(std::cin);
part1(input);
part2(input);
return 0;
}
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