aoc 2025, day 5, part 1

1 files changed, 62 insertions, 0 deletions

diff --git a/2025/src/day05.cpp b/2025/src/day05.cpp
new file mode 100644
index 0000000..2322948
--- /dev/null
+++ b/2025/src/day05.cpp
@@ -0,0 +1,62 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <regex>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using Range  = tuple<long, long>;
+using Ranges = vector<Range>;
+
+tuple<Ranges, vector<long>>
+read_file(const filesystem::path& filename)
+{
+        static const regex range{ R"(^(\d+)-(\d+)$)" };
+        static const regex single{ R"(^(\d+)$)" };
+
+        ifstream file{ filename };
+
+        Ranges       ranges;
+        vector<long> numbers;
+
+        for ( string line; getline(file, line); ) {
+                smatch match;
+                if ( regex_search(line, match, range) ) {
+                        ranges.emplace_back(stol(match[1]), stol(match[2]));
+                }
+                else if ( regex_search(line, match, single) ) {
+                        numbers.emplace_back(stol(match[1]));
+                }
+        }
+
+        return { ranges, numbers };
+}
+
+void
+part1(const Ranges& ranges, const vector<long>& numbers)
+{
+        long count = 0;
+        for ( const auto number: numbers ) {
+                for ( const auto [start, end]: ranges ) {
+                        if ( number >= start && number <= end ) {
+                                ++count;
+                                break;
+                        }
+                }
+        }
+        cout << "Part 1: " << count << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        const auto [ranges, numbers] = read_file("data/day05.txt");
+        part1(ranges, numbers);
+}