Date: 2026-06-06
Time: 16:05
This file solves LeetCode 1684: Count the Number of Consistent Strings. It belongs to a large repository of LeetCode solutions, each in its own directory with a standard structure (solution.py, test_solution.py, plan.md, review.md).
The solution determines how many strings in a list use only characters from a given allowed set.
Solution.countConsistentStringsContract: Given a string allowed of distinct characters and a list words, returns the count of words where every character appears in allowed.
Implementation: Converts allowed to a set for O(1) lookups, then uses sum() over a generator that checks all(c in allowed_set for c in word) for each word. The boolean result of all() is implicitly cast to 0/1 by sum().
findlateststep = countConsistentStringsThis is an alias — the method is bound under a second name. This is a pattern used throughout this repo's test harness: test files import Solution and may call it via an alternative method name. The alias has no semantic relationship to the actual algorithm (the real LeetCode problem "Find Latest Step" is problem 1562, unrelated to this one). It exists purely to satisfy test infrastructure expectations.
sum(generator) over booleans is idiomatic Python for counting truthy values.all(): all() stops iterating the moment it finds a character not in the allowed set, giving an early-exit optimization per word.findlateststep = countConsistentStrings is a class-level attribute assignment that creates a second reference to the same method object.Imports: None — uses only Python builtins (set, all, sum).
Imported by: The "Imported By" list in the prompt shows hundreds of test files across unrelated problem directories. This is an artifact of the test infrastructure — every test file imports Solution from its own directory's solution.py, not from this file. The only genuine consumer is count-the-number-of-consistent-strings/test_solution.py.
1. allowed string → set(allowed) — O(k) where k = len(allowed)
2. For each word in words:
all(c in allowed_set for c in word) — iterates characters, short-circuits on first mismatch3. sum(...) — counts the number of words where all() returned True
4. Returns the integer count
Complexity: O(k + n·m) where k = len(allowed), n = len(words), m = average word length. Space is O(k) for the set.
allowed contains distinct characters (per problem constraints), so the set conversion is a 1:1 mapping.words list returns 0. An empty word "" is always consistent (all() on an empty iterable returns True).None. The method trusts its inputs conform to the LeetCode contract. No validation, no exceptions. This is appropriate — the caller is always the LeetCode judge or the local test harness, both of which guarantee valid inputs.
count-the-number-of-consistent-strings/testsolution.py — See how the test harness exercises this solution and whether it relies on the findlatest_step aliascount-the-number-of-consistent-strings/review.md — Check the code review notes for complexity analysis or alternative approaches consideredfind-words-that-can-be-formed-by-characters/solution.py:countCharacters — A structurally similar problem (character-set membership) that likely uses a frequency-count approach instead of a simple setmethod-aliasing-pattern — Investigate why solution files alias the main method to a second name and how the test harness uses itcheck-if-the-sentence-is-pangram/solution.py — Another set-membership problem with inverted logic (checking that all 26 letters appear)consistent-string-set-lookup — countConsistentStrings converts allowed to a set exactly once, ensuring O(1) per-character membership checks rather than O(k) linear scansall-short-circuits-on-inconsistent — A word with an early disallowed character skips checking remaining characters via all()'s short-circuit behaviorempty-word-always-consistent — An empty string "" counts as consistent because all() returns True on an empty iterablemethod-alias-unrelated — The findlateststep alias has no semantic connection to the algorithm; it exists for test harness compatibility