aoc(2315): Lens Library

1 files changed, 136 insertions, 0 deletions

diff --git a/2023/15/src/part2.cpp b/2023/15/src/part2.cpp
new file mode 100644
index 0000000..4758e86
--- /dev/null
+++ b/2023/15/src/part2.cpp
@@ -0,0 +1,136 @@
+#include <algorithm>
+#include <iostream>
+#include <memory>
+#include <fstream>
+#include <vector>
+#include <array>
+#include <tuple>
+
+#include "util.h"
+
+using Lens = std::pair<std::string,int>;
+using Box = std::vector<Lens>;
+using Boxes = std::array<Box,256>;
+
+struct Cmd
+{
+protected:
+
+    int boxi_;
+    std::string label_;
+
+public:
+
+    Cmd(const std::string& label) : boxi_{ hash(label) }, label_{label}
+    {
+    }
+
+    virtual void apply(Boxes& boxes) const
+    {
+        auto& box = boxes[boxi_];
+        auto has_same_label = [this](const auto& lens) { return lens.first == label_; };
+
+        if (auto lens = std::find_if(box.cbegin(), box.cend(), has_same_label);
+            lens != box.cend())
+        {
+            box.erase(lens);
+        }
+    }
+
+    static int hash(const std::string& label)
+    {
+        int hash{};
+        for (unsigned char c : label)
+        {
+            hash += c;
+            hash *= 17;
+            hash %= 256;
+        }
+        return hash;
+    }
+};
+
+class Add : public Cmd
+{
+    int focal_;
+
+public:
+
+    Add(const std::string& label, int focal) : Cmd(label), focal_{ focal }
+    {
+    }
+
+    void apply(Boxes& boxes) const override
+    {
+        auto& box = boxes[boxi_];
+        auto has_same_label = [this](const auto& lens) { return lens.first == label_; };
+
+        if (auto lens = std::find_if(box.begin(), box.end(), has_same_label);
+            lens != box.end())
+        {
+            lens->second = focal_;
+        }
+        else
+        {
+            box.push_back({ label_, focal_ });
+        }
+    }
+};
+
+int power(const Boxes& boxes)
+{
+    int power{};
+    for (int b = 0; b < boxes.size(); ++b)
+    {
+        for(int l = 0; l < boxes[b].size(); ++l)
+        {
+            power += (b + 1) * (l + 1) * boxes[b][l].second;
+        }
+    }
+    return power;
+}
+
+std::vector<std::unique_ptr<Cmd>> parse(const char* file)
+{
+    using namespace util::separators;
+
+    std::vector<std::unique_ptr<Cmd>> cmds;
+
+    if (std::ifstream input{ file }; input.is_open())
+    {
+        std::string line;
+        std::getline(input,line);
+        std::string_view view{ line };
+
+        auto to_cmd = [&cmds](std::string_view& str)
+        {
+            auto c{ str.find_first_of("=-") };
+            std::string label{ str.substr(0, c) };
+            if (str[c] == '-')
+            {
+                cmds.push_back(std::make_unique<Cmd>(label));
+            }
+            else
+            {
+                int focal = std::stoi( std::string{ str.substr(c + 1) } );
+                cmds.push_back(std::make_unique<Add>(label, focal));
+            }
+        };
+
+        util::accumulate<COMMA>(view, to_cmd);
+    }
+
+    return cmds;
+}
+
+int main(int argc, char* argv[])
+{
+    Boxes boxes;
+    for (const auto& cmd : parse(argv[1]))
+    {
+        cmd->apply(boxes);
+    }
+
+    std::cout << power(boxes) << std::endl;
+    return 0;
+}