69 lines
1.5 KiB
C++
69 lines
1.5 KiB
C++
#include <cstdint>
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#include <iostream>
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#include <vector>
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#include <doctest.h>
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#include <aocpp/Startup.hpp>
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using namespace aocpp;
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namespace {
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auto Step(std::vector<std::uint32_t> & spin, int steps) -> void {
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std::uint32_t cursor = spin.size() - 1;
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for (int i = 0; i < steps; i++) {
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cursor = spin[cursor];
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}
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spin.push_back(spin[cursor]);
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spin[cursor] = spin.size() - 1;
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cursor = spin.size() - 1;
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}
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auto Part1(std::uint64_t jump, std::uint64_t iterations) -> std::uint64_t {
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std::vector<std::uint32_t> spin {0};
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for (int j = 0; j < iterations; j++) {
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Step(spin, jump);
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}
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return spin.back();
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}
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auto Part2(std::uint64_t jump, std::uint64_t iterations) -> std::uint64_t {
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std::uint64_t cursor = 0;
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std::uint64_t after_zero = -1;
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for (std::uint64_t i = 1; i <= iterations; ++i) {
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cursor += jump;
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cursor %= i;
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if (cursor == 0) {
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after_zero = i;
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}
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cursor++;
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}
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return after_zero;
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}
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} // namespace
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TEST_SUITE("2017-17 examples") {
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TEST_CASE("example") {
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std::vector<std::uint32_t> spin {0};
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Step(spin, 3);
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REQUIRE(spin == std::vector<std::uint32_t>{1,0});
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Step(spin, 3);
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REQUIRE(spin == std::vector<std::uint32_t>{2,0,1});
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Step(spin, 3);
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REQUIRE(spin == std::vector<std::uint32_t>{2,0,3,1});
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CHECK(Part1(3, 2017) == 638);
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}
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}
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auto Main(std::istream & in) -> void
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{
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int steps;
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in >> steps;
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std::cout << "Part 1: " << Part1(steps, 2017) << std::endl;
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std::cout << "Part 2: " << Part2(steps, 50'000'000) << std::endl;
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}
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