128 lines
2.9 KiB
C++
128 lines
2.9 KiB
C++
#include <algorithm>
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#include <cstdint>
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#include <iostream>
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#include <iterator>
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#include <numeric>
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#include <sstream>
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#include <stdexcept>
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#include <string>
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#include <tuple>
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#include <vector>
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#include <boost/range/irange.hpp>
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#include <doctest.h>
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#include <aocpp/DivMod.hpp>
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#include <aocpp/Startup.hpp>
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namespace {
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using Input = std::vector<std::int64_t>;
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/// @brief Parse the input stream as a newline-delimited list of lists of integers
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/// @param in input file parsed until EOF
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/// @return outer list of elves, inner lists of calories
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auto Parse(std::istream & in) -> Input
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{
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auto result = Input{};
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using It = std::istream_iterator<std::int64_t>;
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std::copy<It>(in, {}, std::back_inserter(result));
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return result;
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}
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auto Solve(Input const& input, std::size_t const rounds) -> std::int64_t
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{
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auto const len = input.size();
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auto fwds = std::vector<std::size_t>(len);
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auto bwds = std::vector<std::size_t>(len);
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if (len == 0) {
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throw std::runtime_error{"Input too small"};
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}
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auto const zero_it = std::find(input.begin(), input.end(), 0);
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if (zero_it == input.end()) {
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throw std::runtime_error{"no zero element in input"};
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}
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std::iota(fwds.begin(), fwds.end()-1, 1); fwds.back() = 0;
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std::iota(bwds.begin()+1, bwds.end(), 0); bwds.front() = len-1;
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for (auto const _ : boost::irange(rounds)) {
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for (auto const i : boost::irange(len)) {
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// Remove i from the ring
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auto next = fwds[i];
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auto prev = bwds[i];
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fwds[prev] = next;
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bwds[next] = prev;
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auto const steps = aocpp::Mod<std::int64_t>(input[i], len - 1);
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if (steps < len/2) {
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for (auto const _ : boost::irange(steps)) {
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next = fwds[next];
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}
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} else {
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for (auto const _ : boost::irange(len - 1 - steps)) {
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next = bwds[next];
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}
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}
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prev = bwds[next];
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// insert i into the ring
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fwds[i] = next;
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bwds[i] = prev;
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fwds[prev] = i;
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bwds[next] = i;
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}
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}
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auto sum = std::int64_t{0};
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auto cursor = std::distance(input.begin(), zero_it);
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for (auto const _ : boost::irange(3)) {
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for (auto const _ : boost::irange(1000)) {
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cursor = fwds[cursor];
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}
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sum += input[cursor];
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}
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return sum;
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}
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auto Part1(Input const& input) -> std::int64_t
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{
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return Solve(input, 1);
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}
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auto Part2(Input input) -> std::int64_t
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{
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for (auto& x : input) { x *= 811'589'153; }
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return Solve(input, 10);
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}
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} // namespace
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TEST_SUITE("2022-20 examples") {
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TEST_CASE("example") {
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std::istringstream in {
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"1\n"
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"2\n"
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"-3\n"
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"3\n"
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"-2\n"
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"0\n"
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"4\n"};
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auto input = Parse(in);
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CHECK(3 == Part1(input));
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CHECK(1623178306 == Part2(std::move(input)));
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}
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}
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auto Main(std::istream & in, std::ostream & out) -> void
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{
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auto input = Parse(in);
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out << "Part 1: " << Part1(input) << std::endl;
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out << "Part 2: " << Part2(std::move(input)) << std::endl;
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}
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