72 lines
1.7 KiB
C++
72 lines
1.7 KiB
C++
#include <aocpp/Parsing.hpp>
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#include <aocpp/Startup.hpp>
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#include <boost/tuple/tuple.hpp>
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#include <boost/spirit/include/qi.hpp>
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#include <boost/fusion/include/boost_tuple.hpp>
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#include <optional>
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#include <stack>
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namespace qi = boost::spirit::qi;
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namespace {
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auto drop_suffix(std::uint64_t x, std::uint64_t y) -> std::optional<std::uint64_t>
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{
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while (x > 0) {
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if (y == 0) { return x; }
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if (x % 10 != y % 10) return std::nullopt;
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x /= 10;
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y /= 10;
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}
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return std::nullopt;
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}
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auto calibrated(bool const part2, std::uint64_t const target, std::vector<std::uint64_t> const& numbers) -> bool
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{
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if (numbers.size() == 0) { return false; }
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auto work = std::stack<boost::tuple<std::size_t, std::uint64_t>>{};
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work.emplace(numbers.size() - 1, target);
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while (not work.empty())
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{
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auto const [i, t] = work.top();
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work.pop();
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auto const x = numbers[i];
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if (i == 0) {
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if (x == t) { return true; }
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} else {
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if (x < t) { work.emplace(i - 1, t - x); }
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if (t % x == 0) { work.emplace(i - 1, t / x); }
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if (part2) {
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if (auto const u = drop_suffix(t, x)) {
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work.emplace(i - 1, *u);
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}
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}
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}
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}
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return false;
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}
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} // namespace
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auto Main(std::istream & in, std::ostream & out) -> void
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{
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auto const input =
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aocpp::ParseSimple
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<std::vector<boost::tuple<std::uint64_t, std::vector<std::uint64_t>>>>
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(in, *(qi::ulong_long >> ':' >> *(' ' >> qi::ulong_long) >> '\n'));
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std::uint64_t p1 = 0, p2 = 0;
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for (auto && [x, xs] : input) {
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if (calibrated(false, x, xs)) p1 += x;
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if (calibrated(true, x, xs)) p2 += x;
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}
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out << "Part 1: " << p1 << "\n"
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<< "Part 2: " << p2 << "\n";
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}
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