Find Duplicate Files Safely at Scale

Question

The candidate is asked to implement a function to find duplicate files in a file system, providing two helper functions to list directories and check if a path is a directory.

Codemia · Accepted Answer

To find duplicate files in a file system, I will implement a recursive depth-first search (DFS) that traverses the directory structure. The main function, `find_dups(root)`, will utilize two helper functions: `list_dir(root)` to list files and directories, and `is_dir(path)` to check if a path is a directory. I will use a hash map to store file contents or hashes as keys and their corresponding paths as values.

The algorithm works as follows:
1. Initialize an empty hash map to store file contents.
2. Use `list_dir(root)` to iterate through files and directories.
3. For each file, read its content or compute its hash.
4. Check if the content/hash already exists in the map:
   - If it does, append the file path to the existing entry.
   - If not, create a new entry.
5. For directories, recursively call `find_dups` on each subdirectory.

The time complexity of this approach is O(n), where n is the number of files in the directory structure, as each file is processed once. The space complexity is also O(n) due to the storage of file contents in the hash map. However, if files are large, we may need to consider memory usage and optimize by reading files in chunks.

To ensure robustness, I will handle potential errors such as:
- Checking for read permissions before attempting to read a file.
- Handling large files by reading them in chunks to avoid memory overflow.
- Implementing a mechanism to detect and manage circular references (e.g., symlinks) to prevent infinite recursion.

For testing, I would create a variety of test cases, including:
- Directories with no files, single files, and multiple duplicates.
- Cases with symlinks and permission issues.
To optimize, I could consider multi-threading to process files in parallel, especially in large directories, and implement caching for frequently accessed paths.

Find Duplicate Files Safely at Scale

Harvey

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