What is a Collection?

You are given a stream/list of file records, each described as: [FileName, FileSize, [Collection]]. Collections are optional, meaning a file can have zero or more associated collections. The same file can be part of more than one collection.

Build a system that supports:

• Adding or updating file metadata and collection membership.
• Computing the total size of all files in the system.
• Finding the top collections based on size or file-count.

Methods

addFile

void addFile(String fileName, int fileSize, List[String] collections)

• fileName is a Unix-based absolute path including the file name, e.g. /a/b/file1.txt.
• fileSize is in KB, always a positive integer in range [1, 100000].
• collections may contain collection name or may be empty:
  collection names are globally unique and contain lowercase a-z and hyphen '-'
• If addFile is called again with the same fileName, update the stored file size and replace the collections list with the new one.
• When a file’s size or collections are updated, all aggregate stats (total system size, per-collection sizes/counts) must reflect the change.
• Example:

  addFile("/a/b/file1.txt", 400, ["collection-1", "travel-collection-2"])

getTotalFileSize

int getTotalFileSize()

• Return the total size (in KB) of all files currently in the system.
• If a file is updated via addFile, the total size must be incremented/decremented accordingly.
• If no files exist, return 0.

getTopCollections

List<String> getTopCollections(int strategy)

• strategy is always either 0 or 1.
• If strategy = 0: return the top 10 collections sorted by total size of files associated with each collection (descending).
• If strategy = 1: return the top 10 collections sorted by total number of files associated with each collection (descending).
• Ties are broken by choosing the collection name that is lexicographically smaller.
• If fewer than 10 collections exist, return all of them in sorted order.
• A file contributes to every collection it belongs to.

Examples

Example 1: Basic adds, total size, top collections

Router fs = new Router();   conceptual initialization

addFile("/a/b/file1.txt", 400, ["collection-1", "travel-collection-2"]);
addFile("/a/b/file2.txt", 100, ["collection-1"]);
addFile("/c/file3.txt",   200, ["travel-collection-2", "work"]);
addFile("/d/e/file4.txt", 300, []);  no collections

getTotalFileSize()  -> 1000
 total = 400 + 100 + 200 + 300

getTopCollections(0) -> ["travel-collection-2", "collection-1", "work"]
 sizes: travel-collection-2=400+200=600,
        collection-1=400+100=500,
        work=200

getTopCollections(1) -> ["collection-1", "travel-collection-2", "work"]
 counts: collection-1=2 files (file1,file2)
         travel-collection-2=2 files (file1,file3)
         work=1 file (file3)
 tie at count=2 broken lexicographically: "collection-1" < "travel-collection-2"
    

Updating a file changes totals and collection stats

addFile("/a/b/file1.txt", 50, ["work"]);   update existing file1

getTotalFileSize() -> 650
 new total = file1(50) + file2(100) + file3(200) + file4(300) = 650

getTopCollections(0) -> ["work", "travel-collection-2", "collection-1"]
 sizes now:
 work = file3(200) + file1(50) = 250
 travel-collection-2 = file3(200)
 collection-1 = file2(100)

getTopCollections(1) -> ["work", "collection-1", "travel-collection-2"]
 counts now:
 work=2 files (file1,file3)
 collection-1=1 file (file2)
 travel-collection-2=1 file (file3)
 tie at count=1 broken lexicographically: "collection-1" < "travel-collection-2"