1 files changed, 97 insertions, 0 deletions

diff --git a/2023/03/src/part2.cpp b/2023/03/src/part2.cpp
new file mode 100644
index 0000000..16e9678
--- /dev/null
+++ b/2023/03/src/part2.cpp
@@ -0,0 +1,97 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <vector>
+#include <cmath>
+
+using Schematic = std::vector<std::string>;
+using Gears = std::map<std::pair<int,int>,std::vector<int>>;
+
+void check(const Schematic& schematic, Gears& gears, int num, int x, int y)
+{
+    if (x >= 0 and y >= 0 and x < schematic.size()
+        and y < schematic[x].size() and schematic[x][y] == '*')
+    {
+        std::pair<int,int> key{ x, y };
+        if (not gears.count(key))
+        {
+            gears.insert({key, std::vector<int>{}});
+        }
+        gears[key].push_back(num);
+    }
+}
+
+void check_gears(const Schematic& schematic, Gears& gears, int num, int x, int y)
+{
+    int len = 1 + static_cast<int>(std::log10(num));
+    check(schematic, gears, num, x - 1, y - len - 1);
+    check(schematic, gears, num,     x, y - len - 1);
+    check(schematic, gears, num, x + 1, y - len - 1);
+    for (int a = 1; a <= len; ++a)
+    {
+        check(schematic, gears, num, x - 1, y - a);
+        check(schematic, gears, num, x + 1, y - a);
+    }
+    check(schematic, gears, num, x - 1,     y);
+    check(schematic, gears, num,     x,     y);
+    check(schematic, gears, num, x + 1,     y);
+}
+
+Gears find_gears(const Schematic& schematic)
+{
+    Gears gears;
+
+    for (int x = 0; x < schematic.size(); ++x)
+    {
+        const std::string& line = schematic[x];
+
+        int cur{};
+
+        for (int y = 0; y < line.size(); ++y)
+        {
+            if (std::isdigit(line[y]))
+            {
+                cur = 10 * cur + (line[y] - '0');
+            }
+            else
+            {
+                if (cur > 0)
+                {
+                    check_gears(schematic, gears, cur, x, y);
+                }
+                cur = 0;
+            }
+        }
+    }
+
+    return gears;
+}
+
+int main(void)
+{
+    int answer{};
+    Schematic schematic{};
+
+    std::ifstream input{ "resources/input.txt" };
+    if (input.is_open())
+    {
+        std::string line;
+        while (not std::getline(input,line).eof())
+        {
+            line.push_back('.');
+            schematic.push_back(std::move(line));
+        }
+    }
+    input.close();
+
+    Gears gears = find_gears(schematic);
+    for (const auto& [_, vals] : gears) {
+        if (vals.size() == 2)
+        {
+            answer += vals[0] * vals[1];
+        }
+    }
+
+    std::cout << answer << std::endl;
+    return 0;
+}