leetcode 2255. Count Prefixes of a Given String（python）

描述

You are given a string array words and a string s, where words[i] and s comprise only of lowercase English letters.

Return the number of strings in words that are a prefix of s.

A prefix of a string is a substring that occurs at the beginning of the string. A substring is a contiguous sequence of characters within a string.

Example 1:

Input: words = ["a","b","c","ab","bc","abc"], s = "abc"
Output: 3
Explanation:
The strings in words which are a prefix of s = "abc" are:
"a", "ab", and "abc".
Thus the number of strings in words which are a prefix of s is 3.
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Example 2:

Input: words = ["a","a"], s = "aa"
Output: 2
Explanation:
Both of the strings are a prefix of s. 
Note that the same string can occur multiple times in words, and it should be counted each time.
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Note:

1 <= words.length <= 1000
1 <= words[i].length, s.length <= 10
words[i] and s consist of lowercase English letters only.
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解析

根据题意，给定一个字符串数组 words 和一个字符串 s ，其中 words[i] 和 s 仅由小写英文字母组成。返回单词中作为 s 前缀的字符串的数量。

这道题很明显就是考察一个基本的字符串操作，因为我用的是 python ，所以只需要对 words 中的每个元素 word 进行遍历判断即可，只要 s.startswith(word) 为 True ，就对计数器 result 加一，遍历结束后返回 result 即可。

时间复杂度为 O(N) ，空间复杂度为 O(1) 。

解答

class Solution(object):
    def countPrefixes(self, words, s):
        """
        :type words: List[str]
        :type s: str
        :rtype: int
        """
        return sum(1 for word in words if s.startswith(word))	
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运行结果

123 / 123 test cases passed.
Status: Accepted
Runtime: 45 ms
Memory Usage: 13.6 MB
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原题链接

leetcode.com/contest/biw…

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