Unix Find Command

medium · tree traversal, composable filters

Brief-reported interview attribution (unverified): Amazon

Implement the core of the Unix find command over an in-memory file tree. add_dir creates directories (parents as needed); add_file creates a file with a size in bytes (parents as needed). find(path, ...) walks the tree below path and returns every matching path, sorted. Filters combine with AND: name (exact match on the last component), type ("f" for files, "d" for directories), size_gt / size_lt (file size in bytes; a size filter never matches a directory).

class UnixFind:
    def __init__(self):
    def add_dir(self, path):
        # creates all missing directories along the path
    def add_file(self, path, size):
        # creates the file (parents as needed); -> False for an empty/invalid path
    def find(self, path, name=None, type=None, size_gt=None, size_lt=None):
        # -> sorted list of absolute paths that match all given filters
        # (the starting path itself is included when it matches; [] for a missing path)

Rules. A filter that is None is ignored. size_gt/size_lt are strict (size > size_gt, size < size_lt). find on a file path returns that file alone when it matches, and [] when it does not. The root / is a directory and is included in results when it matches.

Tests use explicit inputs and injected clocks/callbacks. No network, real threads or application-server execution is involved.

Public demo

# Public demo: run after implementing the class API above.
f = UnixFind()
for path, size in [('/a/b/f1.txt', 100), ('/a/b/f2.log', 500), ('/a/c/f3.txt', 50), ('/a/readme.md', 1000), ('/d/x.py', 200)]:
    f.add_file(path, size)
print(f.find('/', type='f'))

Starter code

class UnixFind:

    def __init__(self):
        """Initialize the state described in the problem."""
        pass

    def add_dir(self, path):
        """creates all missing directories along the path"""
        pass

    def add_file(self, path, size):
        """creates the file (parents as needed); -> False for an empty/invalid path"""
        pass

    def find(self, path, name=None, type=None, size_gt=None, size_lt=None):
        """-> sorted list of absolute paths that match all given filters (the starting path itself is included when it matches; [] for a missing path)"""
        pass

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