prepare for more puzzles ... :)

1 files changed, 102 insertions, 0 deletions

diff --git a/2023/src/day15.cpp b/2023/src/day15.cpp
new file mode 100644
index 0000000..6fcbfc2
--- /dev/null
+++ b/2023/src/day15.cpp
@@ -0,0 +1,102 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <list>
+#include <numeric>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+string
+read_file(string_view filename)
+{
+        fstream input{ filename };
+        return { istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
+}
+
+void
+rtrim(string& str)
+{
+        str.erase(find_if(str.rbegin(), str.rend(), [](auto chr) { return !isspace(chr); }).base(), str.end());
+}
+
+vector<string>
+split(const string& line, char sep)
+{
+        vector<string> parts{};
+        stringstream   input{ line };
+
+        for ( string part; getline(input, part, sep); ) {
+                rtrim(part);
+                parts.emplace_back(part);
+        }
+
+        return parts;
+}
+
+unsigned int
+calculate_hash(string_view str)
+{
+        unsigned int value = 0;
+        for ( auto chr: str ) {
+                value += static_cast<unsigned char>(chr);
+                value *= 17;
+        }
+        return value % 256;
+}
+
+void
+part1()
+{
+        const auto parts = split(read_file("data/day15.txt"), ',');
+        cout << accumulate(parts.begin(), parts.end(), 0UL, [](auto init, const auto& str) { return init + calculate_hash(str); }) << endl;
+}
+
+void
+part2()
+{
+        vector<list<tuple<string, long>>> boxes(256);
+
+        const auto line  = read_file("data/day15.txt");
+        const auto parts = split(line, ',');
+        for ( const auto& part: parts ) {
+                const auto pos  = part.find_first_of("=-");
+                const auto lens = part.substr(0, pos);
+                auto&      box  = boxes[calculate_hash(lens)];
+
+                if ( part[pos] == '=' ) {
+                        const auto value = stol(part.substr(pos + 1));
+
+                        auto iter = find_if(box.begin(), box.end(), [&lens](const auto& element) { return get<0>(element) == lens; });
+                        if ( iter == box.end() ) {
+                                box.emplace_back(lens, value);
+                        }
+                        else {
+                                get<1>(*iter) = value;
+                        }
+                }
+                else {
+                        box.remove_if([&lens](const auto& element) { return get<0>(element) == lens; });
+                }
+        }
+
+        long value = 0;
+        for ( size_t idx = 0; idx != boxes.size(); ++idx ) {
+                const auto& box = boxes[idx];
+
+                long lens_number = 1;
+                for ( const auto& lens: box ) {
+                        value += static_cast<long>(idx + 1) * lens_number * get<1>(lens);
+                        ++lens_number;
+                }
+        }
+        cout << value << endl;
+}
+
+int
+main()
+{
+        part1();
+        part2();
+}