#7 part 2 on my first try, too. Daaaang.

2022/7/main.cpp

@@ -150,6 +150,25 @@ unsigned long PartOne(File *file, unsigned long &grand_total)
 	return rtn;
 }
 
+void PartTwo(File *file, unsigned long at_least, File *&smallest)
+{
+	Folder *folder = dynamic_cast<Folder*>(file);
+	if(folder)
+	{
+		if(folder->Size() >= at_least && folder->Size() < smallest->Size())
+		{
+			std::cout << "New smallest size of " << folder->Size() << " by folder \""
+			          << folder->Filename() << "\"." << std::endl;
+			smallest = file;
+		}
+
+		for(File *file : folder->Files())
+			PartTwo(file, at_least, smallest);
+	}
+
+	return;
+}
+
 int main()
 {
 	std::ifstream ifs("data.txt");
@@ -226,7 +245,20 @@ int main()
 	unsigned long grand_total = 0;
 	PartOne(&root, grand_total);
 
-	std::cout << "Grand Total: " << grand_total << std::endl;
+	std::cout << "Grand Total (part 1): " << grand_total << std::endl;
+
+	const unsigned long max_space = 70000000;
+	const unsigned long space_needed = 30000000;
+	const unsigned long currently_used = root.Size();
+	const unsigned long currently_unused = max_space - currently_used;
+	const unsigned long amt_to_remove = space_needed - currently_unused;
+
+	File *file_to_remove = &root;
+	PartTwo(&root, amt_to_remove, file_to_remove);
+
+	std::cout << "Remove \"" << file_to_remove->Filename() << "\" to free up "
+	          << file_to_remove->Size() << " which is the smallest amount >= "
+	          << amt_to_remove << " (part 2)." << std::endl;
 
 	return 0;
 }