Update some 2015 sources to .clang-tidy

2015/puzzle-01-02.cc

@@ -2,15 +2,16 @@
 #include <iostream>
 #include <string>
 
-int main(int argc, char** argv)
+auto main() -> int
 {
   for (std::string line; std::getline(std::cin, line);) {
     int floor = 0;
     std::string::size_type pos = 0;
-    for (auto c : line) {
+    for (auto c : line) {  // NOLINT(readability-identifier-length)
       ++pos;
       assert(c == '(' || c == ')');
-      floor += (c == '(') - (c == ')');
+      floor += (c == '(') ? 1 : 0;
+      floor -= (c == ')') ? 1 : 0;
       if (floor == -1) {
         break;
       }