Advent-Of-Code-2024/q1.cpp

#include <algorithm>
#include <fstream>
#include <iostream>
#include <numeric>
#include <sstream>
#include <unordered_map>
#include <vector>

int q1(std::ifstream &in) {
  std::vector<int> l1;
  std::vector<int> l2;

  for (std::string line; std::getline(in, line);) {
    int left, right;
    std::stringstream(line) >> left >> right;

    l1.push_back(left);
    l2.push_back(right);
  }

  std::sort(l1.begin(), l1.end());
  std::sort(l2.begin(), l2.end());

  int sum = 0;
  for (int i = 0; i < l1.size(); i++) {
    sum += abs(l1[i] - l2[i]);
  }
  return sum;
}

int q2(std::ifstream &in) {
  std::vector<int> l1;
  std::unordered_map<int, int> l2;

  for (std::string line; std::getline(in, line);) {
    int left, right;
    std::stringstream(line) >> left >> right;

    l1.push_back(left);
    l2[right]++;
  }

  return std::accumulate(l1.begin(), l1.end(), 0, [&l2](int acc, int curr) {
    return acc + curr * l2[curr];
  });
}

int main() {
  std::ifstream input("i1.txt");
  std::cout << "Part 1: " << q1(input) << std::endl;

  // Could re-read the file, or just seek to the beginning.
  // input = std::ifstream("i1.txt");
  input.clear();
  input.seekg(0);
  std::cout << "Part 2: " << q2(input) << std::endl;
}