16

2019/16.cpp

@@ -0,0 +1,77 @@
+#include <iostream>
+#include <optional>
+#include <vector>
+#include <numeric>
+
+#include <aocpp/Startup.hpp>
+using namespace aocpp;
+
+namespace {
+
+auto FFT(std::size_t start, std::vector<std::int8_t> const& prev)
+{
+  std::vector<std::int8_t> result;
+  std::vector<std::int32_t> partial_sums;
+  auto n = prev.size();
+  result.resize(n);
+  partial_sums.reserve(n+1);
+  partial_sums.push_back(0);
+
+  std::int32_t acc = 0;
+  for (auto const x : prev) {
+    partial_sums.push_back(acc += x);
+  }
+
+  for (std::size_t i = start; i < n+start; i++) {
+    std::int32_t acc = 0;
+    for (std::size_t offset = i; offset < n+start; offset += 4*(i+1)) {
+      acc += partial_sums[std::min(n,offset-start + i + 1)] - partial_sums[std::min(n, offset-start)];
+      acc -= partial_sums[std::min(n, offset-start + 3*(i + 1))] - partial_sums[std::min(n, offset-start + 2*(i + 1))];
+    }
+
+    result[i-start] = std::abs(acc % 10);
+  }
+  return result;
+}
+
+} // namespace
+
+auto main(int argc, char** argv) -> int {
+  auto & in = aocpp::Startup(argc, argv);
+  std::string input;
+  in >> input;
+
+  std::vector<std::int8_t> signal;
+  for (char const c : input) {
+    signal.push_back(c - '0');
+  }
+
+  for (int i = 0; i < 100; i++) {
+    signal = FFT(0, signal);
+  }
+  for (int i = 0; i < 8; i++) {
+    std::cout << int(signal[i]);
+  }
+  std::cout << std::endl;
+
+  signal.clear();
+  signal.reserve(10000 * input.size());
+  for (int i = 0; i < 10000; i++) {
+    for (char const c : input) {
+      signal.push_back(c - '0');
+    }
+  }
+
+  auto offset = std::stol(input.substr(0,7));
+  std::copy(signal.begin() + offset, signal.end(), signal.begin());
+  signal.resize(signal.size() - offset);
+
+  for (int i = 0; i < 100; i++) {
+    signal = FFT(offset, signal);
+  }
+
+  for (auto i = 0; i < 8; i++) {
+      std::cout << int(signal[i]);
+  }
+  std::cout << std::endl;
+}

2019/CMakeLists.txt

@@ -43,6 +43,9 @@ target_link_libraries(14 aocpp)
 add_executable(15 15.cpp)
 target_link_libraries(15 aocpp intcode)
 
+add_executable(16 16.cpp)
+target_link_libraries(16 aocpp)
+
 add_executable(17 17.cpp)
 target_link_libraries(17 aocpp intcode)