2024/1B.cpp


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#include <bits/stdc++.h>
#include "readfile.hpp"


int main(int argc, char const *argv[])
{
	int res = 0;
	std::vector<std::string> file = readfile("1B.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;
}