1 files changed, 87 insertions, 0 deletions

diff --git a/2024/src/day25.cpp b/2024/src/day25.cpp
new file mode 100644
index 0000000..6d43ddf
--- /dev/null
+++ b/2024/src/day25.cpp
@@ -0,0 +1,87 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+using namespace std;
+
+using pattern_type = vector<string>;
+
+vector<string>
+split(string_view line, string_view delimiter)
+{
+        size_t pos_start = 0;
+        size_t pos_end   = 0;
+
+        vector<string> res;
+
+        while ( (pos_end = line.find(delimiter, pos_start)) != std::string::npos ) {
+                auto token = line.substr(pos_start, pos_end - pos_start);
+                pos_start  = pos_end + delimiter.length();
+
+                res.emplace_back(token);
+        }
+
+        res.emplace_back(line.substr(pos_start));
+        return res;
+}
+
+tuple<vector<pattern_type>, vector<pattern_type>>
+read_file(string_view filename)
+{
+        fstream    input{ filename };
+        const auto patterns{ split(string{ istreambuf_iterator<char>{ input }, {} }, "\n\n") };
+
+        vector<pattern_type> keys;
+        vector<pattern_type> locks;
+
+        for ( const auto& pattern: patterns ) {
+                const pattern_type& lines = split(pattern, "\n");
+
+                if ( lines[0] == "#####" && lines[6] == "....." ) {
+                        locks.push_back(lines);
+                }
+                else if ( lines[0] == "....." && lines[6] == "#####" ) {
+                        keys.push_back(lines);
+                }
+        }
+
+        return { keys, locks };
+}
+
+bool
+fits(const pattern_type& key, const pattern_type& lock)
+{
+        for ( size_t row = 0; row != key.size(); ++row ) {
+                for ( size_t col = 0; col != key[row].size(); ++col ) {
+                        if ( key[row][col] == '#' && lock[row][col] == '#' ) {
+                                return false;
+                        }
+                }
+        }
+        return true;
+}
+
+void
+part1(const tuple<vector<pattern_type>, vector<pattern_type>>& data)
+{
+        const auto [keys, locks] = data;
+
+        long count = 0;
+        for ( const auto& key: keys ) {
+                for ( const auto& lock: locks ) {
+                        if ( fits(key, lock) ) {
+                                ++count;
+                        }
+                }
+        }
+        cout << count << endl;
+}
+
+int
+main()
+{
+        const auto data = read_file("data/day25.txt");
+        part1(data);
+}