adding threads to day 6 part 2

Author: K20shores

2024/src/day13.cpp

@@ -149,7 +149,7 @@ int main(int argc, char **argv)
   Data data = parse();
 
   int answer1 = 36870;
-  int64_t answer2 = 0;
+  int64_t answer2 = 78101482023732;
 
   auto first = part1(data);
   std::cout << "Part 1: " << first << std::endl;

2024/src/day14.cpp

@@ -85,7 +85,7 @@ int part2(const Data &data)
     }
   }
   robots = data.robots;
-  iterate(robots, min_t +1, width, height);
+  iterate(robots, min_t + 1, width, height);
   std::vector<std::string> grid(height, std::string(width, '.'));
   for (auto &[px, py, _, __] : robots)
   {
@@ -157,7 +157,7 @@ int main(int argc, char **argv)
   Data data = parse();
 
   int64_t answer1 = 225552000;
-  int64_t answer2 = 0;
+  int64_t answer2 = 7371;
 
   auto first = part1(data);
   std::cout << "Part 1: " << first << std::endl;

2024/src/day6.cpp

@@ -7,6 +7,8 @@
 #include <tuple>
 #include <unordered_set>
 #include <aoc/2024/pos.h>
+#include <thread>
+#include <mutex>
 
 struct Data
 {
@@ -62,16 +64,15 @@ int part2(const Data &data)
 {
   int cycles = 0;
   auto path = data.path;
+  std::mutex mtx;
 
-  for (const auto &obstacle : path)
-  {
+  auto process_obstacle = [&](const Pos &obstacle) {
     std::unordered_set<std::pair<Pos, Pos>, PosPairHash> visited;
-
     Pos p = data.p;
     Pos dir = data.dir;
 
     if (obstacle == p)
-      continue; // ignore the starting location
+      return; // ignore the starting location
     while (true)
     {
       if (visited.find({p, dir}) == visited.end())
@@ -81,6 +82,7 @@ int part2(const Data &data)
       }
       else
       {
+        std::lock_guard<std::mutex> lock(mtx);
         cycles += 1;
         break;
       }
@@ -94,6 +96,17 @@ int part2(const Data &data)
       }
       p += dir;
     }
+  };
+
+  std::vector<std::thread> threads;
+  for (const auto &obstacle : path)
+  {
+    threads.emplace_back(process_obstacle, obstacle);
+  }
+
+  for (auto &thread : threads)
+  {
+    thread.join();
   }
 
   return cycles;