Add 2021 day 15 puzzles

2021-12-15 10:20:08 +00:00
parent f237a6c3fd
commit 0a041cd398
2 changed files with 178 additions and 0 deletions
--- a/2021/puzzle-15-01.cc
+++ b/2021/puzzle-15-01.cc
@@ -0,0 +1,81 @@
+#include <cassert>
+#include <iostream>
+#include <limits>
+#include <string>
+#include <vector>
+
+using UInt = unsigned int;
+
+struct Cost
+{
+  constexpr explicit Cost(UInt entry_cost) : entry_cost_(entry_cost) {}
+
+  [[nodiscard]] constexpr auto entry_cost() const noexcept -> UInt { return entry_cost_; }
+  [[nodiscard]] constexpr auto total_cost() const noexcept -> UInt { return total_cost_; }
+  [[nodiscard]] constexpr auto visited() const noexcept -> bool { return visited_; }
+
+  constexpr void total_cost(UInt total_cost) noexcept { total_cost_ = total_cost; }
+  constexpr void update_total_cost(UInt v) noexcept
+  {
+    total_cost_ = std::min(entry_cost_ + v, total_cost_);
+  }
+  constexpr void visit() noexcept { visited_ = true; }
+
+private:
+  UInt entry_cost_;
+  UInt total_cost_{std::numeric_limits<UInt>::max()};
+  bool visited_{false};
+};
+
+using CostVector = std::vector<Cost>;
+
+auto main() -> int
+{
+  std::string line;
+  CostVector costs;
+  UInt width{0};
+  while (std::getline(std::cin, line) && !line.empty()) {
+    if (width == 0) {
+      width = line.size();
+    }
+    else {
+      assert(width == line.size());
+    }
+    for (auto c : line) {
+      costs.emplace_back(c - '0');
+    }
+  }
+
+  costs[0].total_cost(0);
+
+  while (true) {
+    /* Note that the comparison below makes deliberate use of unsigned wrap-round.  */
+    auto it{costs.begin()};
+    UInt cost{std::numeric_limits<UInt>::max()};
+    for (auto it2{costs.begin()}; it2 != costs.end(); ++it2) {
+      if (!it2->visited() && it2->total_cost() < cost) {
+        cost = it2->total_cost();
+        it = it2;
+      }
+    }
+    it->visit();
+    auto current_cost{it->total_cost()};
+    auto idx{std::distance(costs.begin(), it)};
+    if (idx == costs.size() - 1) {
+      std::cout << "Total cost: " << current_cost;
+      return 0;
+    }
+    if (idx % width != 0) {
+      costs.at(idx - 1).update_total_cost(current_cost);
+    }
+    if ((idx + 1) % width != 0) {
+      costs.at(idx + 1).update_total_cost(current_cost);
+    }
+    if (idx > width) {
+      costs.at(idx - width).update_total_cost(current_cost);
+    }
+    if (idx + width < costs.size()) {
+      costs.at(idx + width).update_total_cost(current_cost);
+    }
+  }
+}
--- a/2021/puzzle-15-02.cc
+++ b/2021/puzzle-15-02.cc
@@ -0,0 +1,97 @@
+#include <cassert>
+#include <iostream>
+#include <limits>
+#include <string>
+#include <vector>
+
+using UInt = unsigned int;
+
+struct Cost
+{
+  constexpr explicit Cost(UInt entry_cost) : entry_cost_(entry_cost) {}
+
+  [[nodiscard]] constexpr auto entry_cost() const noexcept -> UInt { return entry_cost_; }
+  [[nodiscard]] constexpr auto total_cost() const noexcept -> UInt { return total_cost_; }
+  [[nodiscard]] constexpr auto visited() const noexcept -> bool { return visited_; }
+
+  constexpr void total_cost(UInt total_cost) noexcept { total_cost_ = total_cost; }
+  constexpr void update_total_cost(UInt v) noexcept
+  {
+    total_cost_ = std::min(entry_cost_ + v, total_cost_);
+  }
+  constexpr void visit() noexcept { visited_ = true; }
+
+private:
+  UInt entry_cost_;
+  UInt total_cost_{std::numeric_limits<UInt>::max()};
+  bool visited_{false};
+};
+
+using CostVector = std::vector<Cost>;
+
+auto main() -> int
+{
+  std::string line;
+  CostVector costs;
+  UInt width{0};
+  while (std::getline(std::cin, line) && !line.empty()) {
+    if (width == 0) {
+      width = line.size();
+    }
+    else {
+      assert(width == line.size());
+    }
+    for (unsigned i{0}; i < 5; ++i) {
+      for (auto c : line) {
+        UInt cost{c - '0' + i};
+        if (cost > 9) {
+          cost -= 9;
+        }
+        costs.emplace_back(cost);
+      }
+    }
+  }
+  auto initial_size{costs.size()};
+  auto target_size{initial_size * 5};
+  for (auto i{initial_size}; i < target_size; ++i) {
+    auto cost{costs[i - initial_size].entry_cost() + 1};
+    if (cost > 9) {
+      cost -= 9;
+    }
+    costs.emplace_back(cost);
+  }
+
+  costs[0].total_cost(0);
+  width *= 5;
+
+  while (true) {
+    /* Note that the comparison below makes deliberate use of unsigned wrap-round.  */
+    auto it{costs.begin()};
+    UInt cost{std::numeric_limits<UInt>::max()};
+    for (auto it2{costs.begin()}; it2 != costs.end(); ++it2) {
+      if (!it2->visited() && it2->total_cost() < cost) {
+        cost = it2->total_cost();
+        it = it2;
+      }
+    }
+    it->visit();
+    auto current_cost{it->total_cost()};
+    auto idx{std::distance(costs.begin(), it)};
+    if (idx == costs.size() - 1) {
+      std::cout << "Total cost: " << current_cost;
+      return 0;
+    }
+    if (idx % width != 0) {
+      costs[idx - 1].update_total_cost(current_cost);
+    }
+    if ((idx + 1) % width != 0) {
+      costs[idx + 1].update_total_cost(current_cost);
+    }
+    if (idx > width) {
+      costs[idx - width].update_total_cost(current_cost);
+    }
+    if (idx + width < costs.size()) {
+      costs[idx + width].update_total_cost(current_cost);
+    }
+  }
+}