Add 2017 day 14 puzzles.

2017/puzzle-14-01.cc

@@ -0,0 +1,93 @@
+#include <bit>
+#include <iomanip>
+#include <iostream>
+#include <numeric>
+#include <string>
+#include <vector>
+
+using Byte = std::uint8_t;
+using KnotString = std::vector<Byte>;
+
+auto knot_round(KnotString const& in, Byte current_position, Byte length) -> KnotString
+{
+  KnotString rot_left;
+  rot_left.reserve(in.size());
+  std::copy(in.begin() + current_position, in.end(), std::back_inserter(rot_left));
+  std::copy(in.begin(), in.begin() + current_position, std::back_inserter(rot_left));
+
+  std::reverse(rot_left.begin(), rot_left.begin() + length);
+
+  KnotString rot_right;
+  std::copy(rot_left.end() - current_position, rot_left.end(), std::back_inserter(rot_right));
+  std::copy(rot_left.begin(), rot_left.end() - current_position, std::back_inserter(rot_right));
+  return rot_right;
+}
+
+using Knot = std::pair<std::uint64_t, std::uint64_t>;
+
+auto knot(std::string const& rounds) -> Knot
+{
+  /* Put the lengths into a vector.  */
+  std::vector<Byte> lengths;
+  lengths.reserve(rounds.size() + 5);
+  for (auto c : rounds) {
+    lengths.emplace_back(static_cast<Byte>(c));
+  }
+  lengths.emplace_back(17);
+  lengths.emplace_back(31);
+  lengths.emplace_back(73);
+  lengths.emplace_back(47);
+  lengths.emplace_back(23);
+
+  /* Run the hash */
+  Byte current_pos{0};
+  Byte skip{0};
+  std::vector<Byte> string;
+  string.resize(256);
+  std::iota(string.begin(), string.end(), 0);
+
+  for (unsigned i{0}; i < 64; ++i) {
+    for (auto length : lengths) {
+      string = knot_round(string, current_pos, length);
+      current_pos += length + skip;
+      ++skip;
+    }
+  }
+
+  /* Print the dense hash.  */
+  std::uint64_t result0{0};
+  std::uint64_t result1{0};
+  std::uint64_t* hash{&result0};
+  for (unsigned i{0}; i < string.size(); ++i) {
+    if (i % 16 == 0) {
+      if (i == string.size() / 2) {
+        hash = &result1;
+      }
+      *hash <<= 8;
+    }
+    *hash ^= string[i];
+  }
+
+  return {result0, result1};
+}
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read Line\n";
+    return 1;
+  }
+
+  unsigned bit_count{0};
+  for (unsigned i = 0; i < 128; ++i) {
+    std::string key{line};
+    key += '-';
+    key += std::to_string(i);
+    auto [knot1, knot2] = knot(key);
+    bit_count += std::popcount(knot1) + std::popcount(knot2);
+  }
+
+  std::cout << "Population count " << bit_count << '\n';
+  return 0;
+}