2017-17

2017/17.cpp

@@ -0,0 +1,67 @@
+#include <cstdint>
+#include <iostream>
+#include <vector>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+using namespace aocpp;
+
+namespace {
+
+auto Step(std::vector<std::uint32_t> & spin, int steps) -> void {
+  std::uint32_t cursor = spin.size() - 1;
+  for (int i = 0; i < steps; i++) {
+      cursor = spin[cursor];
+    }
+    spin.push_back(spin[cursor]);
+    spin[cursor] = spin.size() - 1;
+    cursor = spin.size() - 1;
+}
+
+auto Part1(std::uint64_t jump, std::uint64_t iterations) -> std::uint64_t {
+  std::vector<std::uint32_t> spin {0};
+  for (int j = 0; j < iterations; j++) {
+    Step(spin, jump);
+  }
+  return spin.back();
+}
+
+auto Part2(std::uint64_t jump, std::uint64_t iterations) -> std::uint64_t {
+  std::uint64_t cursor = 0;
+  std::uint64_t after_zero = -1;
+  for (std::uint64_t i = 1; i <= iterations; ++i) {
+    cursor += jump;
+    cursor %= i;
+    if (cursor == 0) {
+      after_zero = i;
+    }
+    cursor++;
+  }
+
+  return after_zero;
+}
+
+} // namespace
+
+TEST_SUITE("2017-17 examples") {
+  TEST_CASE("example") {
+    std::vector<std::uint32_t> spin {0};
+    Step(spin, 3);
+    REQUIRE(spin == std::vector<std::uint32_t>{1,0});
+    Step(spin, 3);
+    REQUIRE(spin == std::vector<std::uint32_t>{2,0,1});
+    Step(spin, 3);
+    REQUIRE(spin == std::vector<std::uint32_t>{2,0,3,1});
+
+    CHECK(Part1(3, 2017) == 638);
+  }
+}
+
+auto main(int argc, char** argv) -> int {
+  int steps;
+  *Startup(argc, argv) >> steps;
+  std::cout << "Part 1: " << Part1(steps, 2017) << std::endl;
+  std::cout << "Part 2: " << Part2(steps, 50'000'000) << std::endl;
+}

2017/CMakeLists.txt

@@ -19,5 +19,8 @@ target_link_libraries(2017_13 aocpp)
 add_executable(2017_14 14.cpp)
 target_link_libraries(2017_14 aocpp knothash)
 
+add_executable(2017_17 17.cpp)
+target_link_libraries(2017_17 aocpp)
+
 add_executable(2017_18 18.cpp)
 target_link_libraries(2017_18 aocpp)