1455. Check If a Word Occurs As a Prefix of Any Word in a Sentence

#Problem

Given a sentence that consists of some words separated by a single space, and a searchWord, check if searchWord is a prefix of any word in sentence.

Return the index of the word in sentence (1-indexed) where searchWord is a prefix of this word. If searchWord is a prefix of more than one word, return the index of the first word (minimum index). If there is no such word return -1.

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

https://leetcode.com/problems/check-if-a-word-occurs-as-a-prefix-of-any-word-in-a-sentence/

Example 1:

Input: sentence = "i love eating burger", searchWord = "burg"
Output: 4
Explanation: "burg" is prefix of "burger" which is the 4th word in the sentence.

Example 2:

Input: sentence = "this problem is an easy problem", searchWord = "pro"
Output: 2
Explanation: "pro" is prefix of "problem" which is the 2nd and the 6th word in the sentence, but we return 2 as it’s the minimal index.

Example 3:

Input: sentence = "i am tired", searchWord = "you"
Output: -1
Explanation: "you" is not a prefix of any word in the sentence.

Constraints:

• 1 <= sentence.length <= 100
• 1 <= searchWord.length <= 10
• sentence consists of lowercase English letters and spaces.
• searchWord consists of lowercase English letters.

#Test Cases

class Solution:
    def isPrefixOfWord(self, sentence: str, searchWord: str) -> int:

import pytest

from solution import Solution


@pytest.mark.parametrize('sentence, searchWord, expected', [
    ("i love eating burger", "burg", 4),
    ("this problem is an easy problem", "pro", 2),
    ("i am tired", "you", -1),

    ("i love eating burger", "eating", 3),
    ("i love eating burger", "seeing", -1),
    ("i love eating burger", "g", -1),
    ("i love eating burger", "eats", -1),
])
class Test:
    def test_solution(self, sentence, searchWord, expected):
        sol = Solution()
        assert sol.isPrefixOfWord(sentence, searchWord) == expected

#Thoughts

第一反应是用 Trie 树，但单次搜索就没必要了，不等 Trie 建好就查完了。

因为给定的是一个句子，而非单词的数组，肯定要避免做 split 以节省时间和空间。

直接遍历句子中的每一个字符，在每个空格之后跟 searchWord 对齐逐个比对即可。

时间复杂度 O(n)，空间复杂度 O(1)。

#Code

class Solution:
    def isPrefixOfWord(self, sentence: str, searchWord: str) -> int:
        m = len(searchWord)
        idx = 1
        j = 0
        for c in sentence:
            if c == ' ':
                idx += 1
                j = 0
            elif j < m and searchWord[j] == c:
                j += 1
                if j == m:
                    return idx
            else:
                j = m # The idx-th word is not possible.

        return -1