2022-25

2022/25.cpp

@@ -0,0 +1,110 @@
+#include <cstdint> // int64_t
+#include <functional> // plus
+#include <iostream> // istream
+#include <iterator> // istream_iterator
+#include <numeric> // transform_reduce
+#include <sstream> // istringstream
+#include <string> // string
+#include <tuple> // pair, make_pair
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+namespace {
+
+// 
+template <typename T>
+auto DivMod(T dividend, T divisor) -> std::pair<T, T>
+{
+  auto const quotient  = dividend / divisor;
+  auto const remainder = dividend % divisor;
+  if ((remainder >= 0) == (divisor >= 0)) {
+    return {quotient, remainder};
+  } else {
+    return {quotient - 1, remainder + divisor};
+  }
+}
+
+template <typename T>
+auto FromInt(T x) -> std::string
+{
+  std::string output;
+  char const digits[] {"=-012"};
+  while (x != 0) {
+    auto [x_, i] = DivMod<T>(x + 2, 5); // plain % and / are insufficient for negatives
+    x = x_;
+    output.push_back(digits[i]);
+  }
+  std::reverse(output.begin(), output.end());
+  return output;
+}
+
+template <typename T>
+auto ToInt(std::string const& str) -> T
+{
+  T acc {0};
+  for (char c : str) {
+    acc *= 5;
+    switch (c) {
+      case '2': acc += 2; break;
+      case '1': acc += 1; break;
+      case '0': break;
+      case '-': acc -= 1; break;
+      case '=': acc -= 2; break;
+    }
+  }
+  return acc;
+}
+
+auto Solve(std::istream & in) -> std::string
+{
+  using It = std::istream_iterator<std::string>;
+  return FromInt(std::transform_reduce(It(in), It(), 0, std::plus(), ToInt<std::int64_t>));
+}
+
+} // namespace
+
+TEST_SUITE("2022-25 examples") {
+  TEST_CASE("example") {
+    std::istringstream in {
+        "1=-0-2\n"
+        "12111\n"
+        "2=0=\n"
+        "21\n"
+        "2=01\n"
+        "111\n"
+        "20012\n"
+        "112\n"
+        "1=-1=\n"
+        "1-12\n"
+        "12\n"
+        "1=\n"
+        "122\n"
+    };
+    CHECK(Solve(in) == "2=-1=0");
+  }
+  // The example input doesn't test out any negative numbers
+  TEST_CASE("Negative numbers") {
+    CHECK(ToInt<int>("-") == -1);
+    CHECK(ToInt<int>("=") == -2);
+    CHECK(ToInt<int>("-=") == -7);
+    CHECK(ToInt<int>("=-") == -11);
+    CHECK(FromInt(-1) == "-");
+    CHECK(FromInt(-2) == "=");
+    CHECK(FromInt(-7) == "-=");
+    CHECK(FromInt(-11) == "=-");
+  }
+
+  TEST_CASE("DivMod behavior") {
+    CHECK(DivMod<int>(2,5) == std::make_pair(0,2));
+    CHECK(DivMod<int>(-2,5) == std::make_pair(-1,3));
+    CHECK(DivMod<int>(2,-5) == std::make_pair(-1,-3));
+    CHECK(DivMod<int>(-2,-5) == std::make_pair(0,-2));
+  }
+}
+
+auto main(int argc, char** argv) -> int
+{
+  std::cout << "Part 1: " << Solve(*aocpp::Startup(argc, argv)) << std::endl;
+}

2022/CMakeLists.txt

@@ -6,3 +6,6 @@ target_link_libraries(2022_03 aocpp)
 
 add_executable(2022_04 04.cpp)
 target_link_libraries(2022_04 aocpp)
+
+add_executable(2022_25 25.cpp)
+target_link_libraries(2022_25 aocpp)