2185. Counting Words With a Given Prefix

2185. Counting Words With a Given Prefix

Difficulty: Easy

Topics: Array, String, tring Matching

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.

Hint:

1. Go through each word in words and increment the answer if pref is a prefix of the word.

Solution:

We can iterate through the words array and check if the given pref is a prefix of each word. You can use the substr function to check the beginning part of each string and compare it with pref. If they match, you increment the count.

Let's implement this solution in PHP: 2185. Counting Words With a Given Prefix

<?php
/**
 * @param String[] $words
 * @param String $pref
 * @return Integer
 */
function countWordsWithPrefix($words, $pref) {
    ...
    ...
    ...
    /**
     * go to ./solution.php
     */
}

// Example Usage
$words1 = ["pay", "attention", "practice", "attend"];
$pref1 = "at";
echo countWordsWithPrefix($words1, $pref1); // Output: 2

$words2 = ["leetcode", "win", "loops", "success"];
$pref2 = "code";
echo countWordsWithPrefix($words2, $pref2); // Output: 0
?>

Explanation:

1. Function Definition:

   • The function countWordsWithPrefix accepts an array $words and a string $pref.
   • A counter $count is initialized to 0, which will hold the number of words that match the given prefix.

2. Loop Through Words:

   • The function loops through each word in the $words array.

3. Check for Prefix:

   • The substr($word, 0, strlen($pref)) function extracts the first strlen($pref) characters from the word.
   • If this substring matches $pref, the count is incremented.

4. Return Count:

   • Finally, the function returns the total count of words that contain the prefix.

Time Complexity:

• The time complexity is O(n * m), where:
  • n is the number of words in the array.
  • m is the length of the prefix.
  • For each word, we check the first m characters.

This solution is efficient for the input constraints.

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