1 files changed, 76 insertions, 0 deletions

diff --git a/2024/src/day02.cpp b/2024/src/day02.cpp
new file mode 100644
index 0000000..c8ca66f
--- /dev/null
+++ b/2024/src/day02.cpp
@@ -0,0 +1,76 @@
+#include <cstddef>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<vector<long>>
+read_file(string_view filename)
+{
+        fstream              input{ filename };
+        vector<vector<long>> lines;
+
+        auto split = [](const string& str) {
+                stringstream sstr{ str };
+                vector<long> values;
+
+                for ( long value = 0; sstr >> value; ) {
+                        values.emplace_back(value);
+                }
+                return values;
+        };
+
+        for ( string line; getline(input, line); ) {
+                lines.emplace_back(split(line));
+        }
+
+        return lines;
+}
+
+bool
+is_safe(const vector<long>& values)
+{
+        vector<long> diffs;
+        for ( size_t i = 1; i < values.size(); ++i ) {
+                diffs.emplace_back(values.at(i) - values.at(i - 1));
+        }
+
+        auto all_negative = ranges::all_of(diffs, [](auto diff) { return diff >= -3 && diff < 0; });
+        auto all_positive = ranges::all_of(diffs, [](auto diff) { return diff <= 3 && diff > 0; });
+
+        return all_positive || all_negative;
+}
+
+void
+part1(const vector<vector<long>>& lines)
+{
+        cout << ranges::count_if(lines, is_safe) << endl;
+}
+
+void
+part2(const vector<vector<long>>& lines)
+{
+        long safe_count = 0;
+        for ( const auto& line: lines ) {
+                auto         safe = false;
+                for ( size_t i = 0; i != line.size(); ++i ) {
+                        auto copy = line;
+                        copy.erase(copy.begin() + ptrdiff_t(i));
+                        safe |= is_safe(copy);
+                }
+                if ( safe ) {
+                        ++safe_count;
+                }
+        }
+        cout << safe_count << endl;
+}
+
+int
+main()
+{
+        auto lines = read_file("data/day02.txt");
+        part1(lines);
+        part2(lines);
+}