Solutions for 2022 day 20

2022/puzzle-20-02.cc

@@ -0,0 +1,66 @@
+//
+// Created by Matthew Gretton-Dann on 16/12/2022.
+//
+
+#include <array>
+#include <iostream>
+#include <numeric>
+#include <regex>
+#include <stdexcept>
+#include <utility>
+#include <vector>
+
+using Int = std::int64_t;
+using UInt = std::uint64_t;
+using Ints = std::vector<std::pair<Int, Int>>;
+
+using namespace std::string_literals;
+
+auto offset_into(Int dist, Int size)
+{
+  if (dist < 0) {
+    dist += size * (1 - dist / size);
+  }
+  dist %= size;
+  return dist;
+}
+
+auto find_at_offset(Ints const& nums, Int offset) -> Int
+{
+  auto it{std::find_if(nums.begin(), nums.end(), [](auto const& a) { return a.first == 0; })};
+  offset = offset_into(offset + (it - nums.begin()), nums.size());
+  return nums[offset].first;
+}
+
+auto main() -> int
+{
+  std::string line;
+  Ints distances;
+  Int const multiplier{811589153};
+  while (std::getline(std::cin, line)) {
+    distances.emplace_back(
+      std::make_pair(std::stoll(line) * multiplier, static_cast<Int>(distances.size())));
+  }
+
+  Ints nums{distances};
+  std::cout << "Number of numbers: " << nums.size() << "\n";
+  for (unsigned iter{0}; iter < 10; ++iter) {
+    for (auto i : distances) {
+      auto it{nums.erase(std::find(nums.begin(), nums.end(), i))};
+      Int const num_size{static_cast<Int>(nums.size())};
+      Int dist{offset_into(i.first + (it - nums.begin()), num_size)};
+      nums.insert(nums.begin() + dist, i);
+    }
+  }
+
+  Int const num1000{find_at_offset(nums, 1000)};
+  Int const num2000{find_at_offset(nums, 2000)};
+  Int const num3000{find_at_offset(nums, 3000)};
+  Int const result{num1000 + num2000 + num3000};
+  std::cout << "Offset 1000: " << num1000 << "\n";
+  std::cout << "Offset 2000: " << num2000 << "\n";
+  std::cout << "Offset 3000: " << num3000 << "\n";
+  std::cout << "Total: " << result << "\n";
+
+  return EXIT_SUCCESS;
+}