# 2185 Counting Words With a Given Prefix

You are given an array of strings `words` and a string `pref`.

Return the number of strings in `words` that contain `pref` as a prefix.

A prefix of a string `s` is any leading contiguous substring of `s`.

Example 1:

``````Input: words = ["pay","attention","practice","attend"], pref = "at"
Output: 2
Explanation: The 2 strings that contain "at" as a prefix are: "attention" and "attend".
``````

Example 2:

``````Input: words = ["leetcode","win","loops","success"], pref = "code"
Output: 0
Explanation: There are no strings that contain "code" as a prefix.
``````

Constraints:

• `1 <= words.length <= 100`
• `1 <= words[i].length, pref.length <= 100`
• `words[i]` and `pref` consist of lowercase English letters.
 ``````1 2 3 `````` ``````class Solution: def prefixCount(self, words: List[str], pref: str) -> int: return sum(w.startswith(pref) for w in words)``````

Follow-up:
Q: What if the words are sorted lexicographically?
A: We can use binary search twice to locate the lower and upper bounds of the words that have the same prefix. Therefore, the time cost is `O(klogn)`. e.g., Assume `perf = "abcd"`, we can search `"abcd"` and `"abce"` respectively.