# LeetCode 1684. Count the Number of Consistent Strings

## Description

https://leetcode.com/problems/count-the-number-of-consistent-strings/

You are given a string `allowed` consisting of distinct characters and an array of strings `words`. A string is consistent if all characters in the string appear in the string `allowed`.

Return the number of consistent strings in the array `words`.

Example 1:

```Input: allowed = "ab", words = ["ad","bd","aaab","baa","badab"]
Output: 2
Explanation: Strings "aaab" and "baa" are consistent since they only contain characters 'a' and 'b'.
```

Example 2:

```Input: allowed = "abc", words = ["a","b","c","ab","ac","bc","abc"]
Output: 7
Explanation: All strings are consistent.
```

Example 3:

```Input: allowed = "cad", words = ["cc","acd","b","ba","bac","bad","ac","d"]
Output: 4
Explanation: Strings "cc", "acd", "ac", and "d" are consistent.
```

Constraints:

• `1 <= words.length <= 104`
• `1 <= allowed.length <=26`
• `1 <= words[i].length <= 10`
• The characters in `allowed` are distinct.
• `words[i]` and `allowed` contain only lowercase English letters.

## Explanation

Check if all characters are in allowed set.

## Python Solution

``````class Solution:
def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
count = 0

allowed = set(allowed)

for word in words:
i = 0

while i < len(word):
if word[i] not in allowed:
break
i += 1

if i == len(word):
count += 1

return count``````
• Time Complexity: O(N)
• Space Complexity: O(N)