1 files changed, 55 insertions, 0 deletions

diff --git a/2020/src/day01.cpp b/2020/src/day01.cpp
new file mode 100644
index 0000000..d2d8629
--- /dev/null
+++ b/2020/src/day01.cpp
@@ -0,0 +1,55 @@
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <numeric>
+using namespace std;
+
+auto
+read_file(string_view filename)
+{
+        fstream      input{ filename };
+        vector<long> data;
+
+        for ( long value = 0; input >> value; ) {
+                data.emplace_back(value);
+        }
+
+        return data;
+}
+
+void
+process(const vector<long>& values)
+{
+        const long year = 2020;
+
+        if (accumulate(values.begin(), values.end(), 0L) == year) {
+                cout << accumulate(values.begin(), values.end(), 1, multiplies<>()) << endl;
+        }
+}
+
+void
+combination(const vector<long>& values, size_t r)
+{
+        vector<bool> v(values.size());
+        fill(v.end() - long(r), v.end(), true);
+        vector<long> set(r);
+        do {
+                set.clear();
+                for ( size_t i = 0; i != values.size(); ++i ) {
+                        if ( v[i] ) {
+                                set.emplace_back(values[i]);
+                        }
+                }
+                process(set);
+        } while ( std::next_permutation(v.begin(), v.end()) );
+}
+
+int
+main()
+{
+        auto values = read_file("data/day01-sample1.txt");
+        combination(values, 2);
+        combination(values, 3);
+}