1 files changed, 41 insertions, 0 deletions
diff --git a/2024/2.cpp b/2024/2.cpp
new file mode 100644
index 0000000..f6dff14
--- /dev/null
+++ b/2024/2.cpp
@@ -0,0 +1,41 @@
+#include <bits/stdc++.h>
+#include "readfile.hpp"
+
+
+int main(int argc, char const *argv[])
+{
+	int res = 0;
+	std::vector<std::string> file = readfile("2.in");
+	if (file.empty()) {
+		return 1;
+	}
+	std::vector<int> left, right;
+	for (const auto &line : file) {
+		int n1, n2;
+		// put to vector
+		std::istringstream iss(line);
+        if (!(iss >> n1 >> n2)) {
+            std::cerr << "Invalid input line: " << line << std::endl;
+            return 1;
+        }
+        left.push_back(n1);
+        right.push_back(n2);
+	}
+
+	// count
+	if (left.size() != right.size()) {
+		std::cerr << "size mismatch: " << left.size() << " vs " << right.size() << std::endl;
+		return 1;
+	}
+
+    std::map<int, int> rightCount;
+	for (const int &num : right) {
+		rightCount[num]++;
+	}
+
+	for (const int &num : left) {
+		res += num * rightCount[num];
+	}
+	
+	std::cout << res << std::endl;
+}
+\ No newline at end of file