Count Words Using Only Permitted Letters

### Problem `allowed` lists distinct lowercase letters. Count the entries of `words` whose every character appears in allowed. Repeated letters inside a word are permitted. ```cpp class Solution { public: int countConsistentStrings(string allowed, vector<string>& words); }; ``` ### Examples **Example 1:** ```text allowed = "xy", words = ["xx","yx","xyz","z"] Output: 2 Explanation: Only xx and yx use exclusively x and y. ``` **Example 2:** ```text allowed = "m", words = ["m","mm","mn","m"] Output: 3 Explanation: Count duplicate word entries separately. ``` ### Constraints - `1 <= words.length <= 10^4`. - `1 <= allowed.length <= 26`, with distinct letters. - `1 <= words[i].length <= 10`. - Every input character is a lowercase English letter. ### Clarifying Questions Allowed letters may be reused any number of times. Count entries rather than distinct word strings. ```hint Inspect the structure Does `allowed` describe letter membership or a limited supply of letter occurrences? ``` ### Reasoning checkpoints - Apply letter permission as reusable membership, not a consumable inventory. - Count qualifying word entries with their multiplicity, including repeated characters within a word. ### Optional extensions How would a 26-bit mask encode the same membership test?