Number of uniform strings of leetcode simple problem

subject

Give you a string of different characters allowed And an array of strings words . If every character of a string is in allowed in , Call this string Consistent string .
Please return words Array Consistent string Number of .
Example 1：
Input ：allowed = “ab”, words = [“ad”,“bd”,“aaab”,“baa”,“badab”]
Output ：2
explain ： character string “aaab” and “baa” It's all consistent strings , Because they only contain characters ‘a’ and ‘b’ .
Example 2：
Input ：allowed = “abc”, words = [“a”,“b”,“c”,“ab”,“ac”,“bc”,“abc”]
Output ：7
explain ： All strings are consistent .
Example 3：
Input ：allowed = “cad”, words = [“cc”,“acd”,“b”,“ba”,“bac”,“bad”,“ac”,“d”]
Output ：4
explain ： character string “cc”,“acd”,“ac” and “d” Is a consistent string .
Tips ：
1 <= words.length <= 10^4
1 <= allowed.length <= 26
1 <= words[i].length <= 10
allowed The characters in Different from each other .
words[i] and allowed Only lowercase letters .
source ： Power button （LeetCode）

Their thinking

   If words All the characters in the words in allowed If so, the string is consistent , So just ask words The elements and allowed The difference set of , If the difference set is not empty , said words Some of the elements allowed No, , If it is empty , said words There are elements allowed It's all inside .

class Solution:
    def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
        count=0
        for i in words:
            if len(set(i)-set(allowed))==0:
                count+=1
        return count