1408. String Matching in an Array

1408. String Matching in an Array

Difficulty: Easy

Topics: Array, String, String Matching

Given an array of string words, return all strings in words that is a substring of another word. You can return the answer in any order.

A substring is a contiguous sequence of characters within a string

Example 1:

• Input: words = ["mass","as","hero","superhero"]
• Output: ["as","hero"]
• Explanation: "as" is substring of "mass" and "hero" is substring of "superhero". ["hero","as"] is also a valid answer.

Example 2:

• Input: words = ["leetcode","et","code"]
• Output: ["et","code"]
• Explanation: "et", "code" are substring of "leetcode".

Example 3:

• Input: words = ["blue","green","bu"]
• Output: []
• Explanation: No string of words is substring of another string.

Constraints:

• 1 <= words.length <= 100
• 1 <= words[i].length <= 30
• words[i] contains only lowercase English letters.
• All the strings of words are unique.

Hint:

1. Bruteforce to find if one string is substring of another or use KMP algorithm.

Solution:

We need to find all strings in the words array that are substrings of another word in the array, you can use a brute force approach. The approach involves checking each string in the list and verifying if it's a substring of any other string.

Let's implement this solution in PHP: 1408. String Matching in an Array

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

// Example 1
$words = ["mass", "as", "hero", "superhero"];
print_r(stringMatching($words));

// Example 2
$words = ["leetcode", "et", "code"];
print_r(stringMatching($words));

// Example 3
$words = ["blue", "green", "bu"];
print_r(stringMatching($words));
?>

Explanation:

1. The function stringMatching loops through all the words in the input array.
2. For each word, it compares it with every other word in the array using a nested loop.
3. It uses PHP's strpos() function to check if one string is a substring of another. The strpos() function returns false if the substring is not found.
4. If a substring is found, we add the word to the result array and break out of the inner loop, as we only need to record the word once.
5. Finally, the function returns the result array containing all the substrings.

Time Complexity:

• The time complexity is O(n² x m), where n is the number of words and m is the maximum length of a word. This is because we are performing a substring search for each word within every other word.

Example Outputs:

For input ["mass", "as", "hero", "superhero"], the output will be:

Array
(
    [0] => as
    [1] => hero
)

For input ["leetcode", "et", "code"], the output will be:

Array
(
    [0] => et
    [1] => code
)

For input ["blue", "green", "bu"], the output will be:

Array
(
)

This solution works well for the given problem constraints.

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