Day 3

d3/main.cxx

@@ -0,0 +1,116 @@
+#include <iostream>
+#include <algorithm>
+#include <fstream>
+#include <sstream>
+#include <string>
+#include <vector>
+#include <regex>
+#include <unordered_map>
+
+struct Number
+{
+  int value;
+  int row;
+  int start;
+  int end;
+};
+
+struct PairHash
+{
+  template <class T1, class T2>
+  std::size_t operator()(const std::pair<T1, T2> &p) const
+  {
+    auto h1 = std::hash<T1>{}(p.first);
+    auto h2 = std::hash<T2>{}(p.second);
+
+    return h1 ^ h2;
+  }
+};
+
+bool isGear(const char &c)
+{
+  return c == '*';
+}
+
+int main()
+{
+  std::ifstream file{"../d3/input.txt"};
+  std::vector<Number> ns{};
+  std::vector<std::string> inputs{};
+  std::unordered_map<std::pair<int, int>, std::vector<int>, PairHash> gears;
+  std::string line;
+  std::regex pattern("\\d+");
+  int sum{0}, row{0};
+
+  while (std::getline(file, line))
+  {
+    inputs.emplace_back(line);
+
+    auto begin = std::sregex_iterator(line.begin(), line.end(), pattern);
+    auto end = std::sregex_iterator();
+
+    for (std::sregex_iterator i = begin; i != end; i++)
+    {
+      Number n;
+      std::smatch match = *i;
+      n.value = std::stoi(match.str());
+      n.start = match.position();
+      n.end = match.position() + match.str().size() - 1;
+      n.row = row;
+
+      ns.emplace_back(n);
+    }
+    row++;
+  }
+
+  int maxIndex = inputs[0].size() - 1;
+  int inputsSize = inputs.size() - 1;
+
+  for (const auto &n : ns)
+  {
+    int left{std::max(0, n.start - 1)}, right{std::min(n.end + 1, maxIndex)},
+        before{std::max(n.row - 1, 0)}, after{std::min(n.row + 1, inputsSize)};
+
+    if (isGear(inputs[n.row][left]))
+    {
+      gears[std::make_pair(n.row, left)].emplace_back(n.value);
+      continue;
+    }
+    if (isGear(inputs[n.row][right]))
+    {
+      gears[std::make_pair(n.row, right)].emplace_back(n.value);
+      continue;
+    }
+
+    for (auto i{left}; i <= right; i++)
+    {
+      if (isGear(inputs[before][i]))
+      {
+        gears[std::make_pair(before, i)].emplace_back(n.value);
+        continue;
+      }
+      if (isGear(inputs[after][i]))
+      {
+        gears[std::make_pair(after, i)].emplace_back(n.value);
+        continue;
+      }
+    }
+  }
+
+  for (const auto &gear : gears)
+  {
+    if (gear.second.size() == 2)
+    {
+      int product{1};
+      for (const auto &num : gear.second)
+      {
+        product *= num;
+      }
+      sum += product;
+    }
+  }
+
+  std::cout << sum << std::endl;
+
+  return 0;
+}