Try to use more idiomatic C++

q1.cpp

@@ -1,66 +1,57 @@
 #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> l1;
-    std::vector<int> l2;
+  std::vector<int> l2;
 
- //   for (std::string line; std::getline(in, line);) {
+  for (std::string line; std::getline(in, line);) {
- //       std::string left = line.substr(0, line.find(" "));
+    int left, right;
- //       std::string right = line.substr(line.rfind(" "));
+    std::stringstream(line) >> left >> right;
- //       l1.push_back(std::stoi(left));
- //       l2.push_back(std::stoi(right));
- //   }
 
-    for (std::string line; std::getline(in, line);) {
+    l1.push_back(left);
-        int left, right;
+    l2.push_back(right);
-        std::stringstream s(line);
+  }
-        s >> left >> right;
-        l1.push_back(left);
-        l2.push_back(right);
-    }
 
-    std::sort(l1.begin(), l1.end()); 
+  std::sort(l1.begin(), l1.end());
-    std::sort(l2.begin(), l2.end());
+  std::sort(l2.begin(), l2.end());
 
-    int sum = 0;
+  int sum = 0;
-    for (int i = 0; i < l1.size(); i++) {
+  for (int i = 0; i < l1.size(); i++) {
-        sum += abs(l1[i]-l2[i]);
+    sum += abs(l1[i] - l2[i]);
-    }
+  }
-    return sum;
+  return sum;
 }
 
 int q2(std::ifstream &in) {
-    std::vector<int> l1;
+  std::vector<int> l1;
-    std::unordered_map<int, int> l2;
+  std::unordered_map<int, int> l2;
 
-    for (std::string line; std::getline(in, line);) {
+  for (std::string line; std::getline(in, line);) {
-        std::string left = line.substr(0, line.find(" "));
+    int left, right;
-        std::string right = line.substr(line.rfind(" "));
+    std::stringstream(line) >> left >> right;
-        l1.push_back(std::stoi(left));
-        l2[std::stoi(right)]++;
-    }
 
-    std::sort(l1.begin(), l1.end()); 
+    l1.push_back(left);
+    l2[right]++;
+  }
 
-    int sum = 0;
+  return std::accumulate(l1.begin(), l1.end(), 0, [&l2](int acc, int curr) {
-    for (int i = 0; i < l1.size(); i++) {
+    return acc + curr * l2[curr];
-        sum += l1[i] * l2[l1[i]];
+  });
-    }
-    return sum;
 }
 
 int main() {
-    std::ifstream input("i1.txt");
+  std::ifstream input("i1.txt");
-    std::cout << "Part 1: " << q1(input) << std::endl;
+  std::cout << "Part 1: " << q1(input) << std::endl;
 
-    // Could re-read the file, or just seek to the beginning.
+  // Could re-read the file, or just seek to the beginning.
-    // input = std::ifstream("i1.txt");
+  // input = std::ifstream("i1.txt");
-    input.clear();
+  input.clear();
-    input.seekg(0);
+  input.seekg(0);
-    std::cout << "Part 2: " << q2(input) << std::endl;
+  std::cout << "Part 2: " << q2(input) << std::endl;
 }