1 files changed, 58 insertions, 0 deletions

diff --git a/2024/src/day09.cpp b/2024/src/day09.cpp
new file mode 100644
index 0000000..dd25a9d
--- /dev/null
+++ b/2024/src/day09.cpp
@@ -0,0 +1,58 @@
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <string>
+using namespace std;
+
+vector<int>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+        string  line;
+        int     fid = 0;
+
+        getline(input, line);
+
+        vector<int> data;
+        for ( size_t i = 0; i != line.size(); ++i ) {
+                vector<int> values(size_t(line.at(i) - '0'), (i % 2 == 0) ? fid++ : -1);
+                data.insert(data.end(), values.begin(), values.end());
+        }
+        return data;
+}
+
+void
+part1(const vector<int>& data)
+{
+        vector<int> result;
+
+        auto lhs = data.begin();
+        auto rhs = data.end();
+
+        while ( lhs != rhs ) {
+                if ( *lhs != -1 ) {
+                        result.push_back(*lhs);
+                }
+                else {
+                        --rhs;
+                        while ( *rhs == -1 ) {
+                                --rhs;
+                        }
+                        result.push_back(*rhs);
+                }
+                ++lhs;
+        }
+
+        long sum = 0;
+        for ( size_t i = 0; i != result.size(); ++i ) {
+                sum += long(i) * result.at(i);
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto data = read_file("data/day09.txt");
+        part1(data);
+}