Problem statement

A sentence is a list of words separated by single spaces, with no leading or trailing spaces.

Return the 1-based index of the first word in sentence that has searchWord as a prefix. If no word does, return -1.

Example 1

Input: sentence = "i love eating burger", searchWord = "burg"
Output: 4
Explanation: "burger" is the 4th word and starts with "burg".

Example 2

Input: sentence = "this problem is an easy problem", searchWord = "pro"
Output: 2
Explanation: The first match wins, even though the 6th word also matches.

Example 3

Input: sentence = "i am tired", searchWord = "you"
Output: -1

Constraints

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

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

1. Hint 1

   Split on spaces and test each word in order.

2. Hint 2

   A prefix test compares only the first searchWord.length characters.

3. Hint 3

   Return as soon as you find a match — indices are 1-based.

How to solve Check If a Word Occurs As a Prefix of Any Word in a Sentence

Split the sentence into words and run a prefix test on each, left to right, stopping at the first hit.

Approach

1. Split sentence on single spaces.
2. For each word at 0-based index i, compare its first searchWord.length characters with searchWord.
3. Return i + 1 on the first match.
4. Return -1 if the loop finishes.

Why it works

The problem asks for the earliest match, and scanning in order with an early return delivers exactly that.

Complexity

• Time — O(n) over the sentence length
• Space — O(n) for the split

Pitfalls

• Returning the 0-based index is the most common mistake — the answer is 1-based.
• Using a substring search instead of a prefix test matches "pro" inside "approve", which is wrong.
• A word shorter than searchWord can never match; slicing must not go out of bounds.

Reference solution

Python

def isPrefixOfWord(sentence: str, searchWord: str) -> int:
    for i, w in enumerate(sentence.split(" ")):
        if w.startswith(searchWord):
            return i + 1
    return -1

Java

public static int isPrefixOfWord(String sentence, String searchWord) {
    String[] words = sentence.split(" ");
    for (int i = 0; i < words.length; i++) {
        if (words[i].startsWith(searchWord)) return i + 1;
    }
    return -1;
}

C++

int isPrefixOfWord(string sentence, string searchWord) {
    vector<string> words;
    string cur;
    for (char c : sentence) {
        if (c == ' ') { words.push_back(cur); cur.clear(); }
        else cur += c;
    }
    words.push_back(cur);
    for (int i = 0; i < (int) words.size(); i++) {
        if (words[i].size() >= searchWord.size() && words[i].compare(0, searchWord.size(), searchWord) == 0) return i + 1;
    }
    return -1;
}

JavaScript

var isPrefixOfWord = function(sentence, searchWord) {
    const words = sentence.split(" ");
    for (let i = 0; i < words.length; i++) {
        if (words[i].slice(0, searchWord.length) === searchWord) return i + 1;
    }
    return -1;
};

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