Stuff

2020/day_3/toboggan_trajectory.cc

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+#include <fstream>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <utility>
+
+std::vector<std::string> read_input_file() {
+  std::ifstream file("input");
+  std::vector<std::string> data;
+  std::string line;
+
+  while(std::getline(file, line)) 
+    data.push_back(line);
+
+  return data;
+}
+
+int count_trees(const std::vector<std::string> &map, const std::pair<int, int> &slope){
+  int trees = 0;
+
+  int x = slope.first;
+  int y = slope.second;
+  int w = map[0].size();
+  int h = map.size();
+
+  while(y < h) {
+    if(map[y][x%w] == '#') trees++;
+
+    x += slope.first;
+    y += slope.second;
+  }
+
+  return trees;
+}
+
+int solve_a(const std::vector<std::string> &map) {
+  return count_trees(map, {3, 1});
+}
+
+long solve_b(const std::vector<std::string> &map) {
+  std::vector<std::pair<int, int>> slopes {{1, 1}, {3, 1}, {5, 1}, {7, 1}, {1, 2}};
+
+  long result = 1;
+  for(auto& slope: slopes) result *= count_trees(map, slope);
+  return result;
+}
+
+
+int main() {
+  auto data = read_input_file();
+
+  std::cout << solve_a(data) << std::endl;
+  std::cout << solve_b(data) << std::endl;
+
+  return 0;
+}