OOD — File Management System

Implement a simplified in-memory file-management system on HackerRank, with a starter HashMap of folder-name to file-list provided. Required operations: `checkIfFolderExists`, `createFolder`, `createFile`. Edge-case handling matters more than algorithmic depth. Requirements Starter code: a HashMap<String, List<String>> mapping folder name → list of files in that folder. Implement: checkIfFolderExists(name) → boolean createFolder(name) — create a new folder; behaviour on duplicate is one of the edge cases. createFile(folder, filename) — add a file under the named folder; folder must exist (or be created — confirm with the interviewer). Edge cases drive most of the round: duplicates, intermediate folders not yet existing, illegal names. Notes The candidate initially considered a Trie-based hierarchical layout, then matched the simpler HashMap structure the interviewer provided. Stick with the data model the prompt hands you unless extending to deeply-nested directories is part of the spec. For nested-path support (/a/b/c.txt), the natural extension is a tree of folder nodes, each holding its own file list — but this round did not require it. Edge cases that mattered in this round: createFolder("existing") — does it throw, silently no-op, or overwrite? Default to silent no-op unless the spec says otherwise. createFile("unknownFolder", "x") — auto-create the folder, throw, or error-return? The interviewer expected one explicit decision and consistent enforcement. Concurrent createFolder + createFile on the same key — call out the race condition even if not asked. HackerRank runs hidden tests; the reporting candidate had several edge-case failures but was allowed to pass anyway. The interviewer was scoring the design and the reasoning aloud, not the green check marks. Preparation Sketch the three operations in 10 minutes against the provided HashMap. Explicitly state the edge-case decision rule once at the start: "createFolder on existing → no-op; createFile on missing folder → throw". Have the Trie-based variant ready as a follow-up direction ("if the folder hierarchy is nested") — but only pivot if the interviewer asks.