Add solution for 2015 Day 21

src/2015/Day21.cpp

@@ -2,30 +2,117 @@
 
 namespace y2015::day21
 {
-  REGISTER_DAY(2015, Day21, std::vector<int>, int);
+  struct Entity
+  {
+    int hp;
+    int dmg;
+    int armor;
+  };
 
-  REGISTER_TEST_EXAMPLE(2015, Day21, ExampleInput, 1, 0);
-  REGISTER_TEST(2015, Day21, Input, 1, 0);
-  REGISTER_TEST_EXAMPLE(2015, Day21, ExampleInput, 2, 0);
-  REGISTER_TEST(2015, Day21, Input, 2, 0);
+  struct Item
+  {
+    int cost;
+    int dmg;
+    int armor;
+  };
+
+  REGISTER_DAY(2015, Day21, Entity, int);
+
+  REGISTER_TEST(2015, Day21, Input, 1, 91);
+  REGISTER_TEST(2015, Day21, Input, 2, 158);
 
   READ_INPUT(input)
   {
-    std::vector<int> vec;
-    std::string str;
-    while (getline(input, str))
-    {
-    }
-    return vec;
+    Entity monster;
+    input >> "Hit Points: " >> monster.hp >> "\n";
+    input >> "Damage: " >> monster.dmg >> "\n";
+    input >> "Armor: " >> monster.armor >> "\n";
+    return monster;
   }
 
+  bool Win(Entity player, Entity monster)
+  {
+    int playerDmgPerRound = std::max(1, (player.dmg - monster.armor));
+    int monsterDmgPerRound = std::max(1, (monster.dmg - player.armor));
+
+    int i = 0;
+    while (true)
+    {
+      if (i % 2 == 0)
+      {
+        monster.hp -= playerDmgPerRound;
+        if (monster.hp <= 0)
+          return true;
+      }
+      else
+      {
+        player.hp -= monsterDmgPerRound;
+        if (player.hp <= 0)
+          return false;
+      }
+      i++;
+    }
+  }
+
+  std::vector<Item> weapons{Item{8, 4, 0}, Item{10, 5, 0}, Item{25, 6, 0}, Item{40, 7, 0}, Item{74, 8, 0}};
+  std::vector<Item> armors{
+    Item{13, 0, 1}, Item{31, 0, 2}, Item{53, 0, 3}, Item{75, 0, 4}, Item{102, 0, 5}, Item{0, 0, 0}};
+  std::vector<Item> rings{Item{25, 0, 1},
+                          Item{50, 0, 2},
+                          Item{100, 0, 3},
+                          Item{20, 0, 1},
+                          Item{40, 0, 2},
+                          Item{80, 0, 3},
+                          Item{0, 0, 0},
+                          Item{0, 0, 0}};
+
   OUTPUT1(input)
   {
-    return 0;
+    int minCost = std::numeric_limits<int>::max();
+    for (auto& weapon : weapons)
+    {
+      for (auto& armor : armors)
+      {
+        for (int i = 0; i < rings.size(); i++)
+        {
+          for (int j = i + 1; j < rings.size(); j++)
+          {
+            int cost = weapon.cost + armor.cost + rings[i].cost + rings[j].cost;
+            int dmgStat = weapon.dmg + armor.dmg + rings[i].dmg + rings[j].dmg;
+            int armorStat = weapon.armor + armor.armor + rings[i].armor + rings[j].armor;
+            if (cost > minCost)
+              continue;
+            if (Win(Entity{100, dmgStat, armorStat}, input))
+              minCost = cost;
+          }
+        }
+      }
+    }
+    return minCost;
   }
 
   OUTPUT2(input)
   {
-    return 0;
+    int maxCost = 0;
+    for (auto& weapon : weapons)
+    {
+      for (auto& armor : armors)
+      {
+        for (int i = 0; i < rings.size(); i++)
+        {
+          for (int j = i + 1; j < rings.size(); j++)
+          {
+            int cost = weapon.cost + armor.cost + rings[i].cost + rings[j].cost;
+            int dmgStat = weapon.dmg + armor.dmg + rings[i].dmg + rings[j].dmg;
+            int armorStat = weapon.armor + armor.armor + rings[i].armor + rings[j].armor;
+            if (cost < maxCost)
+              continue;
+            if (!Win(Entity{100, dmgStat, armorStat}, input))
+              maxCost = cost;
+          }
+        }
+      }
+    }
+    return maxCost;
   }
 }