Deciphering Uniqueness and Anagram Mysteries with PHP Arrays

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.

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.

A straightforward solution iterates in reverse through each word, comparing it with every other word to check for uniqueness. This brute-force approach results in a time complexity of $O(n^2)$, making it impractical for large datasets, where $n$ is the number of words.

We can capitalize on associative arrays in PHP to efficiently count word occurrences and identify uniqueness:

1. Initialize an associative array for word counts:

   PHP

   $wordCounts = [];

2. Count each word's occurrences as you traverse the list:

   PHP

   foreach ($words as $word) {
       if (isset($wordCounts[$word])) {
           $wordCounts[$word]++;
       } else {
           $wordCounts[$word] = 1;
       }
   }

3. Identify the last unique word by traversing the array from the end:

   PHP

   $lastUniqueWord = "";
   for ($i = count($words) - 1; $i >= 0; $i--) {
       if ($wordCounts[$words[$i]] == 1) {
           $lastUniqueWord = $words[$i];
           break;
       }
   }

4. Return the unique word:

   PHP

   return $lastUniqueWord;

Here is the full code!

<?php
function findLastUniqueWord($words) {
    // Step 1: Initialize an associative array for word counts
    $wordCounts = [];

    // Step 2: Count each word's occurrences as you traverse the list
    foreach ($words as $word) {
        if (isset($wordCounts[$word])) {
            $wordCounts[$word]++;
        } else {
            $wordCounts[$word] = 1;
        }
    }

    // Step 3: Identify the last unique word by traversing the array from the end
    $lastUniqueWord = "";
    for ($i = count($words) - 1; $i >= 0; $i--) {
        if ($wordCounts[$words[$i]] == 1) {
            $lastUniqueWord = $words[$i];
            break;
        }
    }

    // Step 4: Return the unique word
    return $lastUniqueWord;
}

// Example usage
$words = ["apple", "banana", "apple", "orange", "banana", "kiwi"];
echo findLastUniqueWord($words); // Output: kiwi
?>

This approach accomplishes a time complexity of $O(n)$. Iterating through the list twice (once for counting and once for finding uniqueness) is linear, as each operation on an associative array (insert or lookup) generally has an average time complexity of $O(1)$.