Initial commit

2020/puzzle-03-02.cc

@@ -0,0 +1,42 @@
+#include <cassert>
+#include <iostream>
+#include <string>
+#include <vector>
+
+std::string rotate(std::string const &s, std::string::size_type amount) {
+  auto length = s.length();
+  return (s + s).substr(amount % length, length);
+}
+
+int main(int argc, char **argv) {
+  if (argc != 3) {
+    std::cerr << "Usage: " << argv[0] << " <right> <down>\n";
+    return 1;
+  }
+  int right = atoi(argv[1]);
+  int down = atoi(argv[2]);
+  if (right <= 0) {
+    std::cerr << "Right is less than 1\n";
+    return 1;
+  }
+  if (down <= 0) {
+    std::cerr << "Down is less than 1\n";
+    return 1;
+  }
+
+  unsigned count = 0;
+  int row = -1;
+  std::string::size_type rotation = 0;
+  for (std::string line; std::getline(std::cin, line);) {
+    ++row;
+    if ((row % down) != 0) {
+      continue;
+    }
+    auto rotated = rotate(line, rotation);
+    rotation += right;
+    count += (rotated[0] == '#');
+  }
+
+  std::cout << count << "\n";
+  return 0;
+}