1 files changed, 66 insertions, 0 deletions

diff --git a/2023/04/src/part2.cpp b/2023/04/src/part2.cpp
new file mode 100644
index 0000000..1e369d8
--- /dev/null
+++ b/2023/04/src/part2.cpp
@@ -0,0 +1,66 @@
+#include <iostream>
+#include <sstream>
+#include <fstream>
+#include <vector>
+#include <algorithm>
+#include <cmath>
+
+int matchings(const std::string& line, int ws = 10, int ns = 25)
+{
+    int matchings{};
+    std::istringstream in{line};
+
+    int a;
+    std::string skip;
+    in >> skip >> skip;
+
+    std::vector<int> winning(ws);
+    for (int w = 0; w < ws; ++w)
+    {
+        in >> a;
+        winning.push_back(a);
+    }
+
+    in >> skip;
+
+    for (int n = 0; n < ns; ++n)
+    {
+        in >> a;
+        if (std::any_of(winning.cbegin(), winning.cend(), [a](int w){ return w == a; }))
+        {
+            ++matchings;
+        }
+    }
+
+    return matchings;
+}
+
+int main(void)
+{
+    int answer{};
+    std::vector<int> cards;
+
+    std::ifstream input{ "resources/input.txt" };
+    if (input.is_open())
+    {
+        std::string line;
+        while (not std::getline(input,line).eof())
+        {
+            cards.push_back(matchings(line));
+        }
+    }
+    input.close();
+
+    std::vector<int> mult(cards.size(), 1);
+    for (int a = 0; a < cards.size(); ++a)
+    {
+        for (int b = 1; b <= cards[a] and a + b < cards.size(); ++b)
+        {
+            mult[a + b] += mult[a];
+        }
+        answer += mult[a];
+    }
+
+    std::cout << answer << std::endl;
+    return 0;
+}