2 files changed, 70 insertions, 9 deletions

diff --git a/2020/src/day01.cpp b/2020/src/day01.cpp
index d2d8629..67f88c4 100644
--- a/2020/src/day01.cpp
+++ b/2020/src/day01.cpp
@@ -32,24 +32,27 @@ process(const vector<long>& values)
 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);
+        vector<bool> marker(values.size());
+
+        fill(marker.end() - long(r), marker.end(), true);
+
+        vector<long> subset(r);
+
         do {
-                set.clear();
+                subset.clear();
                 for ( size_t i = 0; i != values.size(); ++i ) {
-                        if ( v[i] ) {
-                                set.emplace_back(values[i]);
+                        if ( marker[i] ) {
+                                subset.emplace_back(values[i]);
                         }
                 }
-                process(set);
-        } while ( std::next_permutation(v.begin(), v.end()) );
+                process(subset);
+        } while ( std::next_permutation(marker.begin(), marker.end()) );
 }
 
 int
 main()
 {
-        auto values = read_file("data/day01-sample1.txt");
+        auto values = read_file("data/day01.txt");
         combination(values, 2);
         combination(values, 3);
 }
diff --git a/2020/src/day02.cpp b/2020/src/day02.cpp
new file mode 100644
index 0000000..d7e28f1
--- /dev/null
+++ b/2020/src/day02.cpp
@@ -0,0 +1,58 @@
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <numeric>
+#include <string>
+#include <vector>
+using namespace std;
+
+auto
+read_file(string_view filename)
+{
+        fstream                                 input{ filename };
+        vector<tuple<long, long, char, string>> data;
+
+        for ( string line; getline(input, line); ) {
+                long min = 0;
+                long max = 0;
+                char chr = 0;
+                char password[100];
+                sscanf(line.data(), "%ld-%ld %c: %99s", &min, &max, &chr, password); // NOLINT
+                data.emplace_back(min, max, chr, password);
+        }
+
+        return data;
+}
+
+void
+part1(vector<tuple<long, long, char, string>>& data)
+{
+        long sum = 0;
+        for ( const auto& [min, max, chr, password]: data ) {
+                const auto amount = count(password.begin(), password.end(), chr);
+                if ( min <= amount && amount <= max ) {
+                        ++sum;
+                }
+        }
+        cout << sum << endl;
+}
+
+void
+part2(vector<tuple<long, long, char, string>>& data)
+{
+        long sum = 0;
+        for ( const auto& [min, max, chr, password]: data ) {
+                if ( (password[size_t(min - 1)] == chr) ^ (password[size_t(max - 1)] == chr) ) {
+                        ++sum;
+                }
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto input = read_file("data/day02.txt");
+        part1(input);
+        part2(input);
+}