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

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

Difficulty: Easy

Topics: Two Pointers, String, String Matching

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.

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
• 1
• sentence consists of lowercase English letters and spaces.
• searchWord consists of lowercase English letters.

Hint:

1. First extract the words of the sentence.
2. Check for each word if searchWord occurs at index 0, if so return the index of this word (1-indexed)
3. If searchWord doesn't exist as a prefix of any word return the default value (-1).

Solution:

We can break down the task into the following steps:

1. Split the sentence into individual words.
2. Iterate through the words and check if the searchWord is a prefix of each word.
3. If a word starts with searchWord, return the 1-indexed position of the word.
4. If no word matches, return -1.

Let's implement this solution in PHP: 1455. Check If a Word Occurs As a Prefix of Any Word in a Sentence

<?php /**
 * @param String $sentence
 * @param String $searchWord
 * @return Integer
 */
function isPrefixOfWord($sentence, $searchWord) {
    ...
    ...
    ...
    /**
     * go to ./solution.php
     */
}

// Example Usage:
echo isPrefixOfWord("i love eating burger", "burg");  // Output: 4
echo isPrefixOfWord("this problem is an easy problem", "pro");  // Output: 2
echo isPrefixOfWord("i am tired", "you");  // Output: -1
?>

Explanation:

1. Splitting the Sentence into Words:
   
   We use explode(" ", $sentence) to split the sentence into an array of words.

2. Iterating Over Words:
   
   Use a foreach loop to iterate through each word in the sentence. The $index variable keeps track of the position of the word (0-indexed).

3. Checking for Prefix:
   
   Use strpos($word, $searchWord) === 0 to check if the searchWord occurs at the start of the current word.

4. Returning the Result:
   
   If a match is found, return the 1-based index of the word by adding 1 to $index. If no match is found after the loop, return -1.

Example Outputs:

• For the input sentence = "i love eating burger" and searchWord = "burg", the output is 4 because "burger" is the 4th word.
• For the input sentence = "this problem is an easy problem" and searchWord = "pro", the output is 2 because "problem" is the 2nd word.
• For the input sentence = "i am tired" and searchWord = "you", the output is -1 because no word starts with "you".

Time Complexity:

• Splitting the sentence into words takes O(n), where n is the length of the sentence.
• Checking each word for a prefix takes O(m), where m is the length of the searchWord.
• Thus, the overall time complexity is O(n * m), which is efficient for the input size constraints.

This solution satisfies the constraints and is efficient for the given input size.

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