PHP on LeetCode: How to Solve Problems and Level Up Your Skills

PHP on LeetCode: An Unexpected but Powerful Tool

When you hear "LeetCode," the first associations are Java, Python, or C++. But don't rush to close the tab. PHP isn't just about web forms and WordPress. Modern PHP (starting with versions 7 and 8) is a full-fledged language for solving algorithmic problems. It's fast, concise, and its built-in functions for working with arrays and strings can give many "classic" languages a run for their money.

In this article, we'll break down how to solve problems on LeetCode in PHP, which data structures and algorithms you should learn, and show real code examples. You'll discover why PHP is not a "bug" but a feature for interviews, and how to turn routine into an engaging quest.

Why Solve LeetCode in PHP?

Many people think PHP isn't suitable for algorithms. That's a myth. Here are three reasons why PHP is an excellent choice:

\n
• Rich standard library: array_map, array_filter, array_reduce, explode — these are ready-made building blocks for 80% of problems.
\n
• Flexible typing: You can quickly switch between strings, numbers, and arrays without unnecessary boilerplate.
\n
• Speed: PHP 8 with JIT compilation delivers results comparable to Python, and sometimes faster.
\n

Furthermore, if you're a PHP developer, solving problems on LeetCode directly improves your logical thinking and understanding of the language. You start to see non-obvious possibilities of array_* functions and learn to write efficient, clean code.

What to Learn Before You Start

Before diving into the problem pool, make sure you have the basics down. Here's a list of topics most commonly found in LeetCode problems for PHP:

1. Arrays and Hash Tables

This is the absolute foundation. 90% of problems can be solved by skillfully manipulating arrays. In PHP, arrays are both a list and a dictionary. This gives you a superpower: you can use array_key_exists for O(1) element existence checks.

What to learn:

\n
• array_count_values — counting element frequency.
\n
• array_flip — swapping keys and values (useful for finding duplicates).
\n
• array_unique, array_diff, array_intersect.
\n
• Iteration with index preservation: foreach ($arr as $key => $value).
\n

2. Strings

PHP has historically been strong in string manipulation. Functions like str_split, substr, strpos, and str_replace are your best friends. For problems involving palindromes, anagrams, or character counting, they are indispensable.

Tip: Use strlen() for string length and mb_strlen() for multibyte (Unicode) strings.

3. Linked Lists and Trees

Here, PHP is slightly behind Java/C++ because there are no built-in classes for nodes. But creating your own classes is simple and useful. You'll understand how references and recursion work.

Pattern:

class ListNode {\n    public $val;\n    public $next;\n    public function __construct($val = 0, $next = null) {\n        $this->val = $val;\n        $this->next = $next;\n    }\n}

4. Stack and Queue

PHP doesn't have a separate Stack class, but an array handles it perfectly: array_push() / array_pop() for a stack, array_shift() / array_push() for a queue. For problems like bracket validation or BFS, this is sufficient.

5. Sorting and Searching

The built-in sort() uses quicksort and is very fast. For custom conditions, use usort() with a callback function. Knowledge of binary search (manually or via arra