+day04 part2

2024/day04/part2.cc

@@ -0,0 +1,35 @@
+#include <iostream>
+#include <string>
+
+bool is_xmas(const char upper_left, const char upper_right,
+    const char center, const char lower_left, const char lower_right) {
+  if (center != 'A') {
+    return false;
+  }
+  return upper_left == 'M' && upper_right == 'M' && lower_left == 'S' && lower_right == 'S'
+    || upper_left == 'M' && upper_right == 'S' && lower_left == 'M' && lower_right == 'S'
+    || upper_left == 'S' && upper_right == 'M' && lower_left == 'S' && lower_right == 'M'
+    || upper_left == 'S' && upper_right == 'S' && lower_left == 'M' && lower_right == 'M';
+}
+
+int main() {
+  std::string line[3];
+  int count = 0;
+  int line_number = 0;
+  while (std::getline(std::cin, line[++line_number % 3])) {
+    if (line_number < 3) {
+      continue;
+    }
+    for (int index = 1; index < line[(line_number - 1) % 3].size() - 1; index++) {
+      if (is_xmas(
+            line[(line_number - 2) % 3][index - 1], line[(line_number - 2) % 3][index + 1],
+            line[(line_number - 1) % 3][index],
+            line[line_number % 3][index - 1], line[line_number % 3][index + 1]
+      )) {
+        count++;
+      }
+    }
+  }
+  std::cout << count << std::endl;
+  return EXIT_SUCCESS;
+}