Deciphering Uniqueness and Anagram Mysteries with PHP Arrays

Lesson Introduction

Welcome to our focused exploration of PHP's array functions and their powerful applications in algorithmic challenges. In this lesson, " Deciphering Uniqueness and Anagram Mysteries with PHP Arrays," we'll delve into how these functions can be harnessed to efficiently tackle problems commonly seen in technical interviews.

Problem 1: Unique Echo

Imagine: you’re presented with an extensive list of words, with the task to pinpoint the final word that stands alone — the last non-repeating word. This mirrors the challenge of sorting through a database of unique identifiers to identify a distinct one near the end.

Problem 1: Naive Approach

O(n^2)

Problem 1: Efficient Approach

O(n)

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Problem 2: Efficient Approach

To efficiently find anagrams, we'll assign a sorted character signature to each word, leveraging PHP arrays for efficient lookups:

Create a function to produce sorted character signatures:

PHP

function sortCharacters($input) {
    $characters = str_split($input);
    sort($characters);
    return implode('', $characters);
}

Store signatures from array2 in an associative array for quick comparison:

PHP

$sortedWordsInArray2 = [];
foreach ($array2 as $word) {
    $sortedWordsInArray2[sortCharacters($word)] = true;
}

Find anagrams by comparing each word's signature in array1 with stored signatures:

PHP

$result = [];
foreach ($array1 as $word) {
    $sortedWord = sortCharacters($word);
    if (isset($sortedWordsInArray2[$sortedWord])) {
        $result[] = $word;
    }
}

Return the list of anagrams:
PHP
```
return $result;
```

Here is the full code!

PHP

<?php
function sortCharacters($input) {
    $characters = str_split($input);
    sort($characters);
    return implode('', $characters);
}

function findAnagrams($array1, $array2) {
    // Step 2: Store signatures from array2 in an associative array for quick comparison
    $sortedWordsInArray2 = [];
    foreach ($array2 as $word) {
        $sortedWordsInArray2[sortCharacters($word)] = true;
    }

    // Step 3: Find anagrams by comparing each word's signature in array1 with stored signatures
    $result = [];
    foreach ($array1 as $word) {
        $sortedWord = sortCharacters($word);
        if (isset($sortedWordsInArray2[$sortedWord])) {
            $result[] = $word;
        }
    }

    // Step 4: Return the list of anagrams
    return $result;
}

// Example usage
$array1 = ["listen", "silent", "enlist", "google"];
$array2 = ["inlets", "banana", "google"];

print_r(findAnagrams($array1, $array2)); // Output: Array ( [0] => listen [1] => silent [2] => enlist [3] => google )
?>

This method achieves significant efficiency through the combination of character sorting and associative array lookups. The total complexity is dominated by the sorting operation, which operates in $O(m \log m)$ for each word (where $m$ is the average length of the words). Hence, the overall complexity is $O(n \cdot m \log m + k \cdot m \log m)$ , with $n$ and $k$ being the numbers of words in array1 and array2, respectively.