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Implement cloud storage with quotas and compression

Quick Overview

This question evaluates the ability to design and implement in-memory state management and algorithmic logic for user-scoped storage, including capacity tracking, deterministic eviction policies, file metadata manipulation, and integer/string operations.

Implement cloud storage with quotas and compression

Company: Coinbase

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

## Problem Implement an **in-memory cloud storage** service that supports multiple users, per-user storage quotas, changing quotas with eviction, and file compression/decompression. You are given a list of queries. Each query is an array of strings where the first element is the operation name. Return an array of strings—one result per query. ### Data model - Each **user** has: - a unique `userId` - an integer `capacity` (maximum total size of that user’s files) - zero or more **files** - Each **file** belongs to exactly one user and has: - `fileName` (string) - `size` (positive integer) - File names are unique **per user**. ### Operations All operations are scoped to a user unless stated otherwise. #### 1) `ADD_USER userId capacity` Create a new user. - If `userId` already exists: return `"false"`. - Otherwise: create the user with the given capacity and return `"true"`. #### 2) `ADD_FILE userId fileName size` Add a new file for a user. - If the user does not exist: return `"false"`. - If a file with that name already exists for the user: return `"false"`. - If adding the file would make the user’s total used size exceed the user’s capacity: return `"false"`. - Otherwise add the file and return `"true"`. #### 3) `GET_FILE_SIZE userId fileName` Return the size of a file. - If the user or file does not exist: return `""` (empty string). - Otherwise return the file size as a string. #### 4) `UPDATE_CAPACITY userId newCapacity` Update a user’s capacity. If after the update the user is over capacity, you must **delete existing files** until the total used size is within capacity. Eviction rule: - Repeatedly delete the user’s **largest** file. - If multiple files tie for largest size, delete the one with the **lexicographically largest** `fileName` to make the behavior deterministic. - Stop once total used size \(\le\) `newCapacity`. Return: - If the user does not exist: return `"-1"`. - Otherwise return the **number of files deleted** (as a string). (If no deletion needed, return `"0"`.) #### 5) `COMPRESS_FILE userId fileName` Compress an existing file. - Compression renames the file from `fileName` to `fileName + ".compressed"`. - The compressed file size becomes `size / 2` using **integer division**. Rules: - If user does not exist: return `"false"`. - If `fileName` does not exist: return `"false"`. - If `fileName` already ends with `.compressed`: return `"false"`. - If the target name `fileName + ".compressed"` already exists for that user: return `"false"`. - Otherwise perform the rename and size change and return `"true"`. > Note: Compression reduces used space, so it will never violate capacity. #### 6) `DECOMPRESS_FILE userId compressedName` Decompress an existing compressed file. - Decompression renames `compressedName` to the original name by removing the `.compressed` suffix. - The decompressed file size becomes `size * 2`. Rules: - If user does not exist: return `"false"`. - If `compressedName` does not exist: return `"false"`. - If `compressedName` does **not** end with `.compressed`: return `"false"`. - Let `originalName` be `compressedName` with the final `.compressed` removed. If a file named `originalName` already exists: return `"false"`. - If decompressing would make the user exceed capacity: return `"false"` (and do not change anything). - Otherwise perform the rename and size change and return `"true"`. ### Input/Output format - Input: `queries`, a list of string arrays. - Output: list of strings, one per query. ### Constraints (you may assume) - Number of queries up to ~10^5. - File sizes and capacities fit in 32-bit signed integers. - `userId` and `fileName` are non-empty strings. ### Example (illustrative) Queries: - `["ADD_USER","alice","10"]` → `"true"` - `["ADD_FILE","alice","a.txt","6"]` → `"true"` - `["COMPRESS_FILE","alice","a.txt"]` → `"true"` (now `a.txt.compressed` size 3) - `["DECOMPRESS_FILE","alice","a.txt.compressed"]` → `"true"` (back to size 6) - `["UPDATE_CAPACITY","alice","4"]` → must delete largest files until used \(\le 4\); return number deleted.

Quick Answer: This question evaluates the ability to design and implement in-memory state management and algorithmic logic for user-scoped storage, including capacity tracking, deterministic eviction policies, file metadata manipulation, and integer/string operations.

Process a list of queries for an in-memory cloud storage service. Each user has a storage capacity and a collection of uniquely named files. Support creating users, adding files, reading file sizes, updating capacity with deterministic eviction, and compressing/decompressing files. For UPDATE_CAPACITY, repeatedly delete the user's largest file; if multiple files have the same size, delete the lexicographically largest fileName. Compression renames fileName to fileName + '.compressed' and changes its size to size // 2. Decompression removes the final '.compressed' suffix and changes the size to size * 2. Return one string result for every query in order.

Constraints

0 <= len(queries) <= 10^5
0 <= capacity, newCapacity <= 2^31 - 1
1 <= size <= 2^31 - 1 for ADD_FILE operations
userId and fileName are non-empty strings
File names are unique per user
Compressed sizes use integer division, so a compressed file may become size 0

Examples

Input: ([['ADD_USER', 'alice', '10'], ['ADD_FILE', 'alice', 'a.txt', '6'], ['GET_FILE_SIZE', 'alice', 'a.txt'], ['COMPRESS_FILE', 'alice', 'a.txt'], ['GET_FILE_SIZE', 'alice', 'a.txt'], ['GET_FILE_SIZE', 'alice', 'a.txt.compressed'], ['DECOMPRESS_FILE', 'alice', 'a.txt.compressed'], ['GET_FILE_SIZE', 'alice', 'a.txt'], ['UPDATE_CAPACITY', 'alice', '6']],)

Expected Output: ['true', 'true', '6', 'true', '', '3', 'true', '6', '0']

Explanation: Basic flow: add a user, add a file, compress it, verify the old name disappears and the new name exists with half size, then decompress it back and update capacity without needing deletion.

Input: ([['ADD_USER', 'bob', '20'], ['ADD_FILE', 'bob', 'alpha', '5'], ['ADD_FILE', 'bob', 'beta', '7'], ['ADD_FILE', 'bob', 'gamma', '7'], ['UPDATE_CAPACITY', 'bob', '10'], ['ADD_FILE', 'bob', 'delta', '5'], ['UPDATE_CAPACITY', 'bob', '5'], ['GET_FILE_SIZE', 'bob', 'alpha'], ['GET_FILE_SIZE', 'bob', 'delta']],)

Expected Output: ['true', 'true', 'true', 'true', '2', 'true', '1', '5', '']

Explanation: When capacity drops to 10, the two 7-byte files must be removed; between beta and gamma, gamma is deleted first because it is lexicographically larger. Later alpha and delta tie at size 5, so delta is deleted.

Input: ([['ADD_USER', 'u', '9'], ['ADD_FILE', 'u', 'x', '6'], ['COMPRESS_FILE', 'u', 'x'], ['ADD_FILE', 'u', 'y', '6'], ['DECOMPRESS_FILE', 'u', 'x.compressed'], ['COMPRESS_FILE', 'u', 'y'], ['DECOMPRESS_FILE', 'u', 'x.compressed'], ['GET_FILE_SIZE', 'u', 'x'], ['GET_FILE_SIZE', 'u', 'x.compressed'], ['GET_FILE_SIZE', 'u', 'y.compressed']],)

Expected Output: ['true', 'true', 'true', 'true', 'false', 'true', 'true', '6', '', '3']

Explanation: The first decompression fails because it would exceed capacity. After compressing y, there is enough room, so decompressing x.compressed succeeds.

Input: ([['ADD_FILE', 'ghost', 'a', '1'], ['GET_FILE_SIZE', 'ghost', 'a'], ['UPDATE_CAPACITY', 'ghost', '5'], ['ADD_USER', 'eve', '0'], ['ADD_FILE', 'eve', 'z', '1'], ['COMPRESS_FILE', 'eve', 'missing'], ['DECOMPRESS_FILE', 'eve', 'missing.compressed'], ['ADD_USER', 'eve', '3']],)

Expected Output: ['false', '', '-1', 'true', 'false', 'false', 'false', 'false']

Explanation: Covers missing users, empty-string responses, update on a missing user, zero capacity, missing files, and duplicate user creation.

Input: ([['ADD_USER', 'p', '10'], ['ADD_FILE', 'p', 'a', '6'], ['COMPRESS_FILE', 'p', 'a'], ['ADD_FILE', 'p', 'b', '7'], ['UPDATE_CAPACITY', 'p', '2'], ['GET_FILE_SIZE', 'p', 'a.compressed'], ['GET_FILE_SIZE', 'p', 'b']],)

Expected Output: ['true', 'true', 'true', 'true', '2', '', '']

Explanation: After compressing a, the heap still contains a stale entry for the old uncompressed file. UPDATE_CAPACITY must ignore stale data and delete the current largest valid files until used space is within the new limit.

Input: ([],)

Expected Output: []

Explanation: Edge case: no queries means no results.

Input: ([['ADD_USER', 'odd', '1'], ['ADD_FILE', 'odd', 'f', '1'], ['COMPRESS_FILE', 'odd', 'f'], ['GET_FILE_SIZE', 'odd', 'f.compressed'], ['DECOMPRESS_FILE', 'odd', 'f.compressed'], ['GET_FILE_SIZE', 'odd', 'f']],)

Expected Output: ['true', 'true', 'true', '0', 'true', '0']

Explanation: Compression uses integer division, so a 1-byte file becomes 0 bytes. Decompression then doubles 0 to 0, matching the rules exactly.

Hints

Use a hash map for each user's files so existence checks and size lookups are O(1) on average.
For UPDATE_CAPACITY, a priority queue can give the largest file quickly. Since files may be renamed or deleted, think about lazy deletion of outdated heap entries.

Quick Overview

Implement cloud storage with quotas and compression

Company: Coinbase

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

Constraints

0 <= len(queries) <= 10^5
0 <= capacity, newCapacity <= 2^31 - 1
1 <= size <= 2^31 - 1 for ADD_FILE operations
userId and fileName are non-empty strings
File names are unique per user
Compressed sizes use integer division, so a compressed file may become size 0

Examples

Expected Output: ['true', 'true', '6', 'true', '', '3', 'true', '6', '0']

Expected Output: ['true', 'true', 'true', 'true', '2', 'true', '1', '5', '']

Expected Output: ['true', 'true', 'true', 'true', 'false', 'true', 'true', '6', '', '3']

Explanation: The first decompression fails because it would exceed capacity. After compressing y, there is enough room, so decompressing x.compressed succeeds.

Expected Output: ['false', '', '-1', 'true', 'false', 'false', 'false', 'false']

Explanation: Covers missing users, empty-string responses, update on a missing user, zero capacity, missing files, and duplicate user creation.

Expected Output: ['true', 'true', 'true', 'true', '2', '', '']

Input: ([],)

Expected Output: []

Explanation: Edge case: no queries means no results.

Expected Output: ['true', 'true', 'true', '0', 'true', '0']

Explanation: Compression uses integer division, so a 1-byte file becomes 0 bytes. Decompression then doubles 0 to 0, matching the rules exactly.

Hints

Use a hash map for each user's files so existence checks and size lookups are O(1) on average.
For UPDATE_CAPACITY, a priority queue can give the largest file quickly. Since files may be renamed or deleted, think about lazy deletion of outdated heap entries.